Greater North Sea

Assessment sheet for Greater North Sea sub-region and for five subdivisions

Greater North Sea

Summary

The physical disturbance pressures from mobile bottom-contacting fishing gears varies spatially in the Greater North Sea subregion with 91% of the grid cells (I-2), and 62% of the surface area (I-3), in the depth zone 0-200m, being fished on average per year for the period 2013-2018 (Table 1). Fishing is aggregated with 90% of the pressure occurring in 41% of grid cells (I-4).

The PD method shows an average decline in community biomass of 12% relative to carrying capacity across c-squares (I-6). Most c-squares, 81% (I-7), have an impact score less than 20%. The L1 method shows an average impact of 0.66 across c-squares (I-6). Only 21% (I-7) of the c-squares have impact scores less than 20% (I-7).

Maps of spatial distribution of intensity, seafloor sensitivity and economic value and weight of fisheries landings are shown in Figure 1.

All pressure and impact estimates are for areas < 200 meter depth as there is no longevity prediction for deeper regions.

Table 1

Table 1. Pressure and impact indicators for 2013-2018

Indicators	0 to 200 m	200 to 800 m	more than 800 m
Average intensity (I-1)	2.11	1.76	NA
Proportion of area in fished cells (I-2)	0.91	0.56	NA
Proportion of area fished per year (I-3)	0.62	0.36	NA
Smallest prop. of area in fished cells with 90% of fishing effort (I-4)	0.41	0.22	NA
Proportion of area in unfished cells (I-5)	0.09	0.44	NA
Average PD impact (I-6)	0.12	NA	NA
Average L1 impact (I-6)	0.66	NA	NA
Proportion of area with PD impact < 0.2 (I-7)	0.81	NA	NA
Proportion of area with L1 impact < 0.2 (I-7)	0.21	NA	NA

Figure 1

Figure 1 Geographic distribution of surface abrasion, seabed sensitivity (community longevity) and total value and weight from mobile bottom-contacting gear. The maps of surface abrasion, value and weight show the average per year for 2013-2018

Pressure

The distribution of fishing intensity in the Greater North Sea has a strong spatial variation (Figure 2). Areas of higher intensity occur in the northern North Sea along the edge of the Norwegian Trench and in the eastern English Channel. Areas with lower intensity occur in the western part of the North Sea, and in the deeper parts of the Norwegian trench.

The proportion of area subject to fishing pressure differs between broad-scale habitats and is highest in offshore circalittoral mud (99% of grid cells fished) and circalittoral sand (97% of grid cells fished) (Table 2). Fishing intensity is highest in upper bathyal sediment (average intensity = 1.82 year-1) and offshore circalittoral mud (average intensity = 3.18 year-1).

Total fishing intensity is largely unchanged over time (Figure 3). There is a large peak in intensity in offshore circalittoral mud in 2016, which may be due to erroneous data. Fishing intensity is relatively stable over time in circalittoral sand and offshore circalittoral coarse sediment. The average trawling intensity is more variable over time than the proportion of area fished (Figure 3, compare left and middle panel). This shows that changes in intensity have not affected the spatial distribution of the footprint much.

Fishing pressure is aggregated, both at the regional level as well as at the level of the habitat (Figure 3, right panel). The smallest proportion of habitat with 90% of effort varies between 30-50%. The intensively fished areas represent the ‘core fishing grounds’. These grounds contribute most of the landings and value (Figure 4). Almost 70% of the fishing effort (swept area) and 60% of the landings and value, occur in only 20% of the surface area of the Greater North Sea (Figure 4).

Figure 2

Figure 2 Surface abrasion, Swept Area Ratio, by mobile bottom-contacting gears (year-1), averaged for the 2013-2018 six-year cycle

Table 2

Table 2 Overview of pressure indicators of all mobile bottom-contacting gears per broad-scale habitat averaged for 2013-2018. I refers to the indicators in Table 1.

MSFD broad habitat type	Extent of habitat (1000 km2)	Number of grid cells	Landings 1000 tonnes	Value 106 euro	Swept area 1000 km2	Average intensity (I-1)	Prop. of area in fished grid cells (I-2)	Prop. of area fished per year (I-3)	Smallest prop. of area with 90% of fishing effort (I-4)
Offshore circalittoral sand	242.72	19584	282.28	257.50	437.07	1.80	0.92	0.58	0.36
Offshore circalittoral mud	108.35	9634	149.08	162.24	344.65	3.18	0.99	0.86	0.45
Offshore circalittoral coarse sediment	67.28	7358	77.48	137.96	203.47	3.02	0.95	0.60	0.22
Circalittoral sand	68.39	7591	144.72	146.68	124.75	1.82	0.97	0.71	0.37
Upper bathyal sediment	70.27	4306	44.64	27.08	113.75	1.62	0.53	0.34	0.23
Circalittoral coarse sediment	27.16	4615	25.35	37.26	39.33	1.45	0.83	0.43	0.19
Infralittoral sand	12.36	2647	18.14	30.90	18.60	1.50	0.71	0.51	0.23
Offshore circalittoral mixed sediment	7.32	1753	4.39	8.84	15.58	2.13	0.96	0.64	0.24
Circalittoral mud	5.84	1602	17.74	14.13	11.49	1.97	0.91	0.63	0.19
Unknown	7.88	2192	3.80	13.04	10.92	1.39	0.53	0.32	0.08
Offshore circalittoral rock and biogenic reef	4.08	1912	0.58	1.54	4.53	1.11	0.58	0.34	0.12
Circalittoral mixed sediment	4.88	1416	3.85	3.73	4.07	0.83	0.84	0.40	0.20
Infralittoral coarse sediment	2.68	1138	4.83	7.19	3.41	1.27	0.90	0.56	0.13
Upper bathyal rock and biogenic reef	1.81	656	0.12	0.01	1.62	0.89	0.28	0.23	0.09
Infralittoral mud	1.41	865	0.66	1.93	1.23	0.87	0.40	0.25	0.11
Circalittoral rock and biogenic reef	2.17	1675	0.25	0.66	0.89	0.41	0.65	0.20	0.12
Upper bathyal sediment or Upper bathyal rock and biogenic reef	1.43	483	0.06	0.00	0.76	0.53	0.29	0.20	0.05
Infralittoral rock and biogenic reef	1.04	1417	0.30	0.62	0.51	0.49	0.54	0.16	0.08
Infralittoral mixed sediment	1.24	627	0.03	0.04	0.05	0.04	0.35	0.03	0.11

Figure 3

Figure 3. Time series of (a) mean fishing intensity (surface abrasion), (b) proportion of the surface area of the seafloor fished, (c) aggregation of fishing (proportion of the surface area with 90% of the fishing effort) by habitat. Results represent vessels over 15m (2009-2011) and vessels over 12m (2012-2018).

Figure 4

Figure 4. Cumulative proportion of the swept area, landings and value. Grid cells were sorted from highest to lowest fishing intensity and include non-fished cells. The results are for all mobile bottom-contacting gears based on averaged fishing data per c-square from 2013-2018.

Core fishing grounds

Core fishing grounds are defined as the c-squares with the 90% highest value of landings in the VMS data. Figure 5 shows the number of years c-squares are within the 90% highest value by métier. If fishing in a métier occurs in the same c-square every year with high value of landings, the rightmost bar in Figure 5 and 6 will be high, meaning that the c-square is within the 90% highest value of landings every year during the period 2013-2018. If a c-square is only within the 90% highest value in one year, it will end up in the bar at the left. Figure 6 shows the percentage area overlap between the 90% highest value per year and the reference fishing ground. Both figures highlight that the fisheries for small pelagic fish (OT_SPF) and the seine (SSC_DMF, SDN_DMF) have the highest variation in space.

Figure 7 illustrates the relationship between area fished in percent and the cumulated value of landings, sorted from the c-squares with highest value fisheries. The curves are generally starting steeply, illustrating the concentration of the fisheries at fishing grounds and the curves are ending horizontally, illustrating the peripheral fisheries going on outside the main fishing grounds.

Figure 5

Figure 5. Number of years c-squares are within the 90% core fishing grounds by metier during the period 2013-2018

Figure 6

Figure 6. Percentage area overlap between the 90% highest value per year and the reference core fishing ground

Figure 7

Figure 7. Percent area fished vs. landings value (euro) by métier, coloured by year

Fishing by métier

Intensity, weight and value of landings are estimated for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers (Table 3).

The métier with the highest landings and value per area fished is the beam trawl fishery for whelks, snails and scallop (TBB_MOL) but note that only a very small area has been fished by this métier. The seines (SDN_DMF and SSC_DMF) have the lowest landings and value per area fished. This is followed by otter trawls that target crustaceans (OT_CRU).

Table 3

Table 3. Overview of area fished (sum of swept area), landings and value for the different metiers. Area fished in 1000 km², weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Area swept (1000 km2)	9.45	205.10	553.74	28.20	17.87	146.54	218.50	55.04	109.30	0.02
Landings (1000 tonnes)	42.32	22.69	494.89	12.19	92.27	8.83	22.35	26.09	64.54	1.80
Value (10^6 euro)	99.55	92.44	247.55	29.33	16.39	17.20	44.51	94.54	234.99	2.47
Landings (1000 tonnes)/Area swept (1000 km2)	4.48	0.11	0.89	0.43	5.16	0.06	0.10	0.47	0.59	87.42
Value (10^6 euro)/Area swept (1000 km2)	10.53	0.45	0.45	1.04	0.92	0.12	0.20	1.72	2.15	119.84

Impact

The impact of mobile bottom-contacting fishing from the PD method shows the areas of highest fishing impact along the slopes of the Norwegian trench in the Skagerrak and western Norway and in the eastern English Channel (note the 200m depth limit in this assessment) (Figure 8, left). High impact areas are also seen along the continental coast of the North Sea, in the southern North Sea and Kattegat. High impact from the L1 method covers a much larger area (Figure 8, right) that mimics the map of fishing intensity.

The impact scores are largely constant over time (Figure 9, left panel). Impact varies between habitats (Figure 8 shows the four most extensive habitat types). Of these four habitat types, impact is highest in offshore circalittoral mud and lowest in offshore circalittoral sand. Between 50-80% of each habitat type has a PD impact score <0.2, whereas only 10-40% of each habitat type has an L1 impact score <0.2.

Table 4 shows impact per métier relative to weight and value of landings. In this analysis, the different métiers are assessed for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers. As such this estimates the maximum impact compared to the untrawled situation and the impact estimated assuming all other métiers to have impacted the habitat will be less than this. The métier with the highest impact (PD and L1) relative to the value and landings is the otter trawl fishery for crustaceans (OT_CRU) and the seines ( SDN_DMF and SSC_DMF). The beam trawl fishery for whelks, snails and scallop (TBB_MOL) has the lowest impact per value and landings but note that only a very small area has been fished by this métier (Table 3).

Métiers differ in their habitat association and impact on each habitat type (Figure 10). Fishing impact on mud is dominated by the otter trawl fishery (OT_CRU and OT_DMF). Beam trawl impact mostly occurs in circalittoral sand. The two impact indicators are typically showing similar qualitative patterns but differ in predicted impact of OT_CRU and OT_DMF. These differences arise as the PD method uses a four times larger depletion rate for OT_CRU compared with OT_DMF due to a larger gear penetration depth, whereas the L1 method assumes that all fauna are sensitive to bottom trawl disturbance (independent of the gear penetration depth).

Figure 8

Figure 8. Impact of mobile bottom-contacting gears averaged for the 2013-2018 six-year cycle for the PD and L1 method.

Figure 9

Figure 9. The mean impact of mobile bottom-contacting gears in all combined MSFD habitats and the four most extensive habitat types between 2009 and 2018 (left). The proportion of the fished area with an impact of less than 0.2 (right)

Table 4

Table 4. Overview of impact per metier relative to weight and value of landings estimated for the grid cells fished (SAR >0) with these métiers only. Weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Landings (1000 tonnes)/PD impact	0.326	0.016	0.422	0.084	3.358	0.073	0.081	0.136	0.064	8.276
Value (10^6 euro)/PD impact	0.766	0.070	0.210	0.203	0.809	0.142	0.162	0.493	0.234	11.346
Landings (1000 tonnes)/L1 impact	0.055	0.004	0.031	0.011	0.078	0.004	0.004	0.022	0.010	1.412
Value (10^6 euro)/L1 impact	0.130	0.017	0.016	0.026	0.019	0.008	0.008	0.081	0.038	1.936

Figure 10

Figure 10. PD impact (upper panel) and L1 impact (lower panel) of selected gear groupings on the most extensive MSFD habitat types. Impact is estimated in isolation of the other gear groupings. Note the different scales on the Y-axis.

Management scenarios

The figures and tables below show one implementation of multi-purpose habitat management through reductions in effort and spatial closures for the four most extensive MSFD habitat types. They show the changes in average impact (PD, L1), unfished area and fisheries values of landings based on a static assessment of effort removal.

The analysis is based on the progressive removal of 5 to 99% of all MBCG fishing effort, starting from the c-squares with the lowest effort (corrected for the areal extent of the MSFD habitat within each c-square). Blue dots show the current situation and are used as reference. The % of unfished area in the reference is only based on grid cells that are unfished. Average PD and L1 impacts are a weighted average and consider the areal extent of each MSFD habitat type within a grid cell.

Note that the fraction of grid cells above/below a certain impact threshold initially remains the same (not shown) as the removal of effort starts from the c-squares with the lowest effort that typically have low impact.

MSFD habitat - 1

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.08	0.63	8.37	100.00	100.00
5	0.08	0.49	45.38	92.54	93.32
10	0.07	0.40	57.53	85.28	87.28
15	0.07	0.32	65.83	77.80	81.45
20	0.06	0.26	72.35	69.45	75.49
30	0.05	0.18	81.69	52.02	62.92
40	0.04	0.12	87.83	38.69	52.18
60	0.02	0.05	94.93	20.73	29.49
80	0.01	0.02	98.40	7.55	9.53
99	0.00	0.00	99.97	0.10	0.06

MSFD habitat - 2

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.19	0.85	1.37	100.00	100.00
5	0.18	0.68	27.28	91.71	91.06
10	0.17	0.57	39.98	84.07	82.25
15	0.16	0.49	49.06	77.18	75.47
20	0.15	0.42	56.46	70.96	70.17
30	0.13	0.31	68.27	59.27	59.66
40	0.10	0.22	76.91	48.48	50.22
60	0.06	0.11	89.27	28.17	33.78
80	0.02	0.03	96.77	9.15	17.58
99	0.00	0.00	99.96	0.10	0.21

MSFD habitat - 3

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.14	0.65	4.76	100.00	100.00
5	0.12	0.47	51.48	92.33	90.62
10	0.11	0.37	62.07	85.93	80.76
15	0.10	0.31	68.54	79.70	70.49
20	0.10	0.26	73.75	73.86	64.37
30	0.08	0.19	81.25	61.54	51.47
40	0.06	0.13	86.57	49.73	38.78
60	0.04	0.06	93.66	27.89	21.88
80	0.01	0.02	98.12	10.35	7.70
99	0.00	0.00	99.97	0.50	0.35

MSFD habitat - 4

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.13	0.76	2.57	100.00	100.00
5	0.12	0.64	30.89	94.42	96.18
10	0.11	0.55	42.49	88.81	92.43
15	0.10	0.47	51.29	82.03	88.18
20	0.09	0.40	58.97	77.55	84.89
30	0.08	0.29	70.73	68.22	78.57
40	0.07	0.20	79.42	58.77	72.07
60	0.04	0.09	90.51	39.41	56.21
80	0.02	0.03	96.75	19.54	11.70
99	0.00	0.00	99.93	0.49	0.23

Overview all MSFD habitats

Fishing effort consequences, as a % relative to total swept area, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral sand	242.72	0.0	<0.1	0.3	1.4	3.4	6.6	11.3	18.1	27.8	44.6
Offshore circalittoral mud	108.35	0.1	0.8	2.9	5.9	10.0	15.6	22.7	31.8	44.2	61.5
Offshore circalittoral coarse sediment	67.28	<0.1	<0.1	0.4	1.1	2.3	4.5	8.9	16.4	28.0	48.2
Circalittoral sand	68.39	<0.1	0.3	1.8	4.7	8.8	14.2	20.8	29.3	40.9	58.8
Upper bathyal sediment	70.27	0.0	<0.1	0.6	4.8	11.0	19.5	29.7	41.2	54.1	71.4
Circalittoral coarse sediment	27.16	0.0	0.0	<0.1	0.2	1.1	3.5	7.3	13.1	22.5	37.8
Infralittoral sand	12.36	0.0	0.0	0.0	<0.1	0.3	3.4	11.8	24.5	42.9	65.1
Offshore circalittoral mixed sediment	7.32	<0.1	<0.1	0.7	2.4	5.5	10.9	18.8	29.5	42.5	63.4
Circalittoral mud	5.84	0.0	<0.1	0.7	3.1	6.4	11.6	18.5	26.4	38.0	58.1
Unknown	7.88	0.0	0.0	0.0	0.0	0.0	<0.1	0.7	3.9	12.6	36.9
Offshore circalittoral rock and biogenic reef	4.08	0.0	0.0	0.0	0.0	<0.1	0.9	3.2	9.1	23.1	52.1
Circalittoral mixed sediment	4.88	0.0	0.0	<0.1	0.5	1.8	5.7	11.9	19.2	30.7	51.4
Infralittoral coarse sediment	2.68	0.0	<0.1	0.2	1.2	5.0	14.3	22.8	34.3	48.9	66.4
Upper bathyal rock and biogenic reef	1.81	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	2.2	19.7
Infralittoral mud	1.41	0.0	0.0	0.0	0.0	0.0	0.0	<0.1	0.7	11.5	37.0
Circalittoral rock and biogenic reef	2.17	0.0	0.0	0.0	0.0	0.2	1.5	3.9	10.6	21.8	42.4
Upper bathyal sediment or Upper bathyal rock and biogenic reef	1.43	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.1	18.0
Infralittoral rock and biogenic reef	1.04	0.0	0.0	0.0	0.0	0.0	<0.1	0.5	1.4	4.6	17.3
Infralittoral mixed sediment	1.24	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.3	5.3	16.8

Fishing value consequences, as a % relative to total value, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral sand	242.72	0.0	<0.1	0.6	2.3	5.2	9.8	16.7	27.3	44.4	66.3
Offshore circalittoral mud	108.35	0.3	1.4	4.9	9.8	16.0	23.5	32.3	42.7	56.0	73.3
Offshore circalittoral coarse sediment	67.28	<0.1	<0.1	0.6	2.0	4.0	7.0	12.5	22.0	36.3	60.4
Circalittoral sand	68.39	<0.1	0.4	2.1	5.2	9.9	17.2	23.2	31.1	42.0	59.5
Upper bathyal sediment	70.27	0.0	<0.1	0.4	5.9	12.5	24.1	35.2	47.9	63.0	82.8
Circalittoral coarse sediment	27.16	0.0	<0.1	<0.1	0.3	1.8	5.1	13.7	20.1	29.7	44.4
Infralittoral sand	12.36	0.0	0.0	0.0	<0.1	0.5	4.9	13.2	39.0	55.3	72.9
Offshore circalittoral mixed sediment	7.32	<0.1	0.1	1.1	3.6	8.5	15.9	27.1	40.1	54.0	72.1
Circalittoral mud	5.84	0.0	<0.1	0.8	3.5	7.9	14.7	22.1	31.7	44.4	66.2
Unknown	7.88	0.0	0.0	0.0	0.0	0.0	<0.1	0.8	3.3	10.0	32.6
Offshore circalittoral rock and biogenic reef	4.08	0.0	0.0	0.0	0.0	<0.1	1.4	5.2	14.0	36.0	73.2
Circalittoral mixed sediment	4.88	0.0	<0.1	<0.1	0.5	1.8	5.4	12.3	21.9	36.2	57.8
Infralittoral coarse sediment	2.68	0.0	<0.1	0.2	1.9	10.3	36.0	49.6	58.8	70.0	75.7
Upper bathyal rock and biogenic reef	1.81	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	94.1	95.2
Infralittoral mud	1.41	0.0	0.0	0.0	0.0	0.0	0.0	<0.1	1.5	18.9	55.0
Circalittoral rock and biogenic reef	2.17	0.0	0.0	0.0	0.0	0.3	2.2	5.3	17.3	26.2	50.0
Upper bathyal sediment or Upper bathyal rock and biogenic reef	1.43	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	4.0	100.0
Infralittoral rock and biogenic reef	1.04	0.0	0.0	0.0	0.0	0.0	<0.1	1.0	3.4	10.5	23.3
Infralittoral mixed sediment	1.24	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.5	4.4	15.3

Fishing weight consequences, as a % relative to total weight, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral sand	242.72	<0.1	<0.1	0.7	2.2	4.8	8.6	14.2	22.5	34.0	52.0
Offshore circalittoral mud	108.35	0.3	1.4	5.5	11.3	17.8	25.1	32.8	42.1	53.8	67.5
Offshore circalittoral coarse sediment	67.28	<0.1	0.1	0.9	2.5	4.6	8.6	16.5	31.6	46.9	69.3
Circalittoral sand	68.39	<0.1	0.3	1.5	3.6	6.7	11.5	15.7	21.0	28.6	42.8
Upper bathyal sediment	70.27	<0.1	<0.1	0.7	2.8	8.7	16.5	27.3	42.3	53.1	71.0
Circalittoral coarse sediment	27.16	0.0	<0.1	<0.1	0.7	2.3	6.6	15.4	21.9	31.6	50.3
Infralittoral sand	12.36	0.0	0.0	0.0	<0.1	0.5	5.8	13.5	39.1	52.5	69.2
Offshore circalittoral mixed sediment	7.32	<0.1	0.2	1.5	5.4	11.3	19.9	31.3	43.7	54.5	70.9
Circalittoral mud	5.84	<0.1	<0.1	0.3	2.3	6.1	10.0	13.0	79.7	84.5	90.9
Unknown	7.88	<0.1	<0.1	<0.1	<0.1	<0.1	0.1	1.5	4.5	13.4	38.5
Offshore circalittoral rock and biogenic reef	4.08	<0.1	<0.1	<0.1	<0.1	0.1	2.5	7.8	19.1	43.4	75.9
Circalittoral mixed sediment	4.88	0.0	<0.1	<0.1	0.4	1.8	4.9	10.1	16.6	26.8	46.0
Infralittoral coarse sediment	2.68	0.0	<0.1	0.2	1.7	11.6	40.7	52.5	59.1	71.1	77.9
Upper bathyal rock and biogenic reef	1.81	0.0	0.0	0.0	0.0	0.0	0.0	0.0	<0.1	5.0	30.2
Infralittoral mud	1.41	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	3.0	22.2	65.0
Circalittoral rock and biogenic reef	2.17	<0.1	<0.1	<0.1	<0.1	0.5	2.5	5.7	26.0	34.2	62.9
Upper bathyal sediment or Upper bathyal rock and biogenic reef	1.43	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	0.2	14.0
Infralittoral rock and biogenic reef	1.04	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	1.6	3.9	13.0	25.5
Infralittoral mixed sediment	1.24	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.3	3.9	16.6

Northern North Sea

Summary

The physical disturbance pressures from mobile bottom-contacting fishing gears greatly varies over space within the Northern North Sea subdivision with an average of 91% of the grid cells (I-2), and 57% of the surface area (I-3) being fished between 2013 and 2018 at an overall average intensity of 2.01 year-1 (I-1) (Table 1). A total of 9% of the grid cells are unfished and they mainly located north of the Dogger Bank and east of England. Fishing is aggregated with 90% of the pressure occurring in 38% of grid cells (I-4).

The PD method shows an average decline in community biomass of 7% relative to carrying capacity across c-squares (I-6). A large proportion of c-squares, 91% (I-7), have an impact score less than 20%. The L1 method shows an average impact of 0.60 across c-squares (I-6). Only 23% (I-7) of the c-squares have impact scores less than 20% (I-7). The average impact calculated by the PD method is the lowest among the Greater North Sea subdivisions, with the largest proportion of grid cells impacted below 20%. The average impact calculated with the L1 method is still high, but high scores may be influenced by the high seafloor sensitivity linked to longevity, according to which the eastern half of the Northern North Sea has high sensitivity because of longevity classes above 6 years (Figure 1).

Maps of spatial distribution of intensity, seafloor sensitivity and economic value and weight of fisheries landings are shown in Figure 1. Average value across the Northern North Sea shows a wide distribution of value but the largest proportion coming from the northern half of the subdivision. Landings show hotspots located along the Norwegian Trench and in several other spots offshore.

All pressure and impact estimates are for areas < 200 metre depth as there is no longevity prediction layer for deeper regions.

Table 1

Table 1. Pressure and impact indicators for 2013-2018

Indicators	0 to 200 m	200 to 800 m	more than 800 m
Average intensity (I-1)	2.01	NA	NA
Proportion of area in fished cells (I-2)	0.91	NA	NA
Proportion of area fished per year (I-3)	0.57	NA	NA
Smallest prop. of area in fished cells with 90% of fishing effort (I-4)	0.38	NA	NA
Proportion of area in unfished cells (I-5)	0.09	NA	NA
Average PD impact (I-6)	0.07	NA	NA
Average L1 impact (I-6)	0.60	NA	NA
Proportion of area with PD impact < 0.2 (I-7)	0.91	NA	NA
Proportion of area with L1 impact < 0.2 (I-7)	0.23	NA	NA

Figure 1

Figure 1 Geographic distribution of surface abrasion, seabed sensitivity (community longevity) and total value and weight from mobile bottom-contacting gear. The maps of surface abrasion, value and weight show the average per year for 2013-2018

Pressure

The distribution of fishing intensity in the Northern North Sea greatly is spatially heterogeneous (Figure 2). Areas of higher intensity occur east of the Shetland Islands and along the Norwegian Trench, matching with the fishing intensity observed in the latter subdivision. Areas with lower intensity occur in the southern part of the Northern North Sea, especially east of England north of the Dogger Bank where no fishing is occurring.

Fishing intensity differs between broad-scale habitats and is highest in upper bathyal sediment (average intensity = 15.89 year-1), offshore circalittoral mud (average intensity = 3.28 year-1) and offshore circalittoral mixed sediments (average intensity = 2.27 year-1). For these habitats, the proportion of area subject to fishing pressure is 100%, 99% and 98%, respectively. Offshore circalittoral mud is also one of the top two habitats by mean swept area, which, together with offshore circalittoral sand, they account for most of the landing and value.

Figure 3 displays fishing intensity and proportion of area fished over time. If the large peaks around 2016-2017 are not considered, as they might derive from erroneous data, fishing intensity does not show a clear pattern over time. A mostly constant pattern is also visible in the proportion of area fished and in the proportion of area containing 90% of the effort (the core fishing grounds). The most intensely and extensively fished habitat is offshore circalittoral mud.

Fishing pressure is aggregated, both at the regional level as well as at the level of the habitat (Figure 3, right panel). The smallest proportion of habitat with 90% of effort is similar between broad-scale habitats quantifying between 40-50%. The intensively fished areas represent the ‘core fishing grounds’. These grounds contribute most of the landings and value (Figure 4). More than 60% of the fishing effort (swept area), landings and value occur in less than 20% of the surface area of the Northern North Sea (Figure 4).

Figure 2

Figure 2 Surface abrasion, Swept Area Ratio, by mobile bottom-contacting gears (year-1), averaged for the 2013-2018 six-year cycle

Table 2

Table 2 Overview of pressure indicators of all mobile bottom-contacting gears per broad-scale habitat averaged for 2013-2018. I refers to the indicators in Table 1.

MSFD broad habitat type	Extent of habitat (1000 km2)	Number of grid cells	Landings 1000 tonnes	Value 106 euro	Swept area 1000 km2	Average intensity (I-1)	Prop. of area in fished grid cells (I-2)	Prop. of area fished per year (I-3)	Smallest prop. of area with 90% of fishing effort (I-4)
Offshore circalittoral sand	164.94	12043	163.98	103.12	278.55	1.69	0.88	0.50	0.33
Offshore circalittoral mud	62.21	5243	90.85	68.73	204.16	3.28	0.99	0.85	0.46
Offshore circalittoral coarse sediment	25.27	2889	29.56	14.84	30.24	1.20	0.92	0.42	0.26
Upper bathyal sediment	0.31	99	3.11	1.13	4.91	15.89	1.00	1.00	0.61
Offshore circalittoral mixed sediment	1.44	345	1.06	1.58	3.27	2.27	0.98	0.61	0.22
Circalittoral sand	1.34	291	0.13	0.31	0.50	0.38	0.76	0.24	0.19
Circalittoral coarse sediment	0.72	279	0.12	0.40	0.40	0.56	0.92	0.36	0.19
Circalittoral mud	0.75	157	0.04	0.15	0.30	0.40	0.84	0.31	0.20
Unknown	0.42	286	0.07	0.12	0.19	0.45	0.67	0.24	0.17
Offshore circalittoral rock and biogenic reef	0.31	391	0.10	0.17	0.19	0.61	0.96	0.34	0.25
Circalittoral rock and biogenic reef	0.52	269	0.07	0.13	0.12	0.22	0.82	0.17	0.25
Circalittoral mixed sediment	0.17	77	0.01	0.02	0.04	0.23	0.69	0.20	0.23
Infralittoral rock and biogenic reef	0.15	180	0.02	0.03	0.02	0.16	0.75	0.12	0.22
Infralittoral sand	0.22	99	0.00	0.01	0.02	0.07	0.41	0.07	0.14
Infralittoral coarse sediment	0.05	80	0.00	0.01	0.01	0.21	0.72	0.17	0.18
Infralittoral mud	0.06	34	0.00	0.00	0.00	0.02	0.21	0.02	0.18
Infralittoral mixed sediment	0.02	15	0.00	0.00	0.00	0.02	0.25	0.02	NA

Figure 3

Figure 3. Time series of (a) mean fishing intensity (surface abrasion), (b) proportion of the surface area of the seafloor fished, (c) aggregation of fishing (proportion of the surface area with 90% of the fishing effort) by habitat. Results represent vessels over 15m (2009-2011) and vessels over 12m (2012-2018).

Figure 4

Figure 4. Cumulative proportion of the swept area, landings and value. Grid cells were sorted from highest to lowest fishing intensity and include non-fished cells. The results are for all mobile bottom-contacting gears based on averaged fishing data per c-square from 2013-2018.

Core fishing grounds

Core fishing grounds are defined as the c-squares with the 90% highest value of landings in the VMS data. Figure 5 shows the number of years c-squares are within the 90% highest value by métier. If fishing in a métier occurs in the same c-square every year with high value of landings, the rightmost bar in Figure 5 and 6 will be high, meaning that the c-square is within the 90% highest value of landings every year during the period 2013-2018. If a c-square is only within the 90% highest value in one year, it will end up in the bar at the left. Figure 6 shows the percentage area overlap between the 90% highest value per year and the reference fishing ground. Majority of the active métiers in the Norther North Sea show consistent levels of variability in core fishing grounds among years with limited grid cells overlap. The métier that shows the most stability in core fishing ground over time is otter trawl for demersal fish (OT_DMF).

Such temporal variability is reflected in Figure 7. Figure 7 illustrates the relationship between area fished in percent and the cumulated value of landings, sorted from the c-squares with highest value fisheries. The curves are generally starting steeply, illustrating the concentration of the fisheries at fishing grounds and the curves are ending horizontally, illustrating the peripheral fisheries going on outside the main fishing grounds.

Figure 5

Figure 5. Number of years c-squares are within the 90% core fishing grounds by metier during the period 2013-2018

Figure 6

Figure 6. Percentage area overlap between the 90% highest value per year and the reference core fishing ground

Figure 7

Figure 7. Percent area fished vs. landings value (euro) by métier, coloured by year

Fishing by métier

Intensity, weight and value of landings are estimated for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers (Table 3).

The métier with the lowest landings and value per area fished are the seines (SDN_DMF and SSC_DMF). Otter trawl targeting crustaceans and demersal fish have intermediate landing and value per area swept (OT_CRU, OT_DMF). The highest value per area is given by dredges for mussels and scallops (DRB_MOL) although a limited area was swept compared to other active métiers.

Table 3

Table 3. Overview of area fished (sum of swept area), landings and value for the different metiers. Area fished in 1000 km², weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Area swept (1000 km2)	1.85	32.92	301.75	1.62	3.31	90.42	88.69	0.01	2.40	0
Landings (1000 tonnes)	2.64	5.13	250.17	0.31	14.77	1.64	11.91	<0.005	2.58	0
Value (10^6 euro)	6.20	15.75	134.36	1.27	2.49	2.39	23.39	0.01	4.97	0
Landings (1000 tonnes)/Area swept (1000 km2)	1.43	0.16	0.83	0.19	4.46	0.02	0.13	0.44	1.07	NaN
Value (10^6 euro)/Area swept (1000 km2)	3.36	0.48	0.45	0.78	0.75	0.03	0.26	0.9	2.07	NaN

Impact

The impact of mobile bottom-contacting fishing from the PD method shows the areas of highest fishing impact are located along the slopes of the Norwegian trench and in some locations along the coast of UK and east of the Shetland Islands (Figure 8, left). A much larger area with high impact was identified using the L1 method, possibly due to the high seabed sensitivity calculated for the eastern half of the Northern North Sea considering longevity. Areas with less impact are matching with low fishing or no fishing areas seen in Figure 1 (Figure 8, right).

Once the large drop in 2017 is not considered, the impact scores seem to be largely constant over time (Figure 9, left panel). Impact varies between habitats according to the L1 method, but they have similar scores according to the PD method (Figure 8 shows the four most extensive habitat types). Of the four most extensive habitat types, impact is highest in offshore circalittoral mud, which also has the lowest portion of area subject to an impact lower than 0.2. A much larger proportion of areas with impact lower than 0.2 is estimated for each habitat according to the PD method.

Table 4 shows impact per métier relative to weight and value of landings. In this analysis, the different métiers are assessed for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers. As such this estimates the maximum impact compared to the untrawled situation and the impact estimated assuming all other métiers to have impacted the habitat will be less than this. The métier with the highest impact (PD and L1) relative to the value and landings are the seines (SDN_DMF, SSC_DMF) and the otter trawl for crustaceans (OT_CRU) because only limited landings derived from a large area being fished. The dredges for mussel and scallop (DRB_MOL) seems to have the lowest impact per value but it is important to consider the small area being swept, while the otter trawl for demersal fish (OT_DMF) has the lowest impact per landing and value among the métiers that swept the largest proportion of area (Table 3).

Métiers differ in their habitat association and impact on each habitat type (Figure 10). Fishing impact on offshore circalittoral mud is dominated by the otter trawl fishery (OT_CRU and OT_DMF). Fishing impact on offshore circalittoral sand is dominated by métiers targeting demersal fish (OT_DMF, SSC_DMF). Seines shows highest impact on offshore circalittoral mixed sediments. The two impact indicators are typically showing similar qualitative patterns but differ in predicted impact of OT_CRU and OT_DMF. These differences arise as the PD method uses a four times larger depletion rate for OT_CRU compared with OT_DMF due to a larger gear penetration depth, whereas the L1 method assumes that all fauna are sensitive to bottom trawl disturbance (independent of the gear penetration depth).

Figure 8

Figure 8. Impact of mobile bottom-contacting gears averaged for the 2013-2018 six-year cycle for the PD and L1 method.

Figure 9

Figure 9. The mean impact of mobile bottom-contacting gears in all combined MSFD habitats and the four most extensive habitat types between 2009 and 2018 (left). The proportion of the fished area with an impact of less than 0.2 (right)

Table 4

Table 4. Overview of impact per metier relative to weight and value of landings estimated for the grid cells fished (SAR >0) with these métiers only. Weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Landings (1000 tonnes)/PD impact	0.095	0.023	0.377	0.031	4.484	0.028	0.097	0.074	0.080	NA
Value (10^6 euro)/PD impact	0.222	0.071	0.203	0.123	0.812	0.040	0.190	0.151	0.153	NA
Landings (1000 tonnes)/L1 impact	0.013	0.004	0.030	0.003	0.096	0.002	0.004	0.009	0.010	NA
Value (10^6 euro)/L1 impact	0.031	0.012	0.016	0.014	0.017	0.003	0.008	0.018	0.019	NA

Figure 10

Figure 10. PD impact (upper panel) and L1 impact (lower panel) of selected gear groupings on the most extensive MSFD habitat types. Impact is estimated in isolation of the other gear groupings. Note the different scales on the Y-axis.

Management scenarios

The figures and tables below show one implementation of multi-purpose habitat management through reductions in effort and spatial closures for the four most extensive MSFD habitat types. They show the changes in average impact (PD, L1), unfished area and fisheries values of landings based on a static assessment of effort removal.

The analysis is based on the progressive removal of 5 to 99% of all MBCG fishing effort, starting from the c-squares with the lowest effort (corrected for the areal extent of the MSFD habitat within each c-square). Blue dots show the current situation and are used as reference. The % of unfished area in the reference is only based on grid cells that are unfished. Average PD and L1 impacts are a weighted average and consider the areal extent of each MSFD habitat type within a grid cell.

Note that the fraction of grid cells above/below a certain impact threshold initially remains the same (not shown) as the removal of effort starts from the c-squares with the lowest effort that typically have low impact.

The most extensive habitat by area in the Northern North Sea is offshore circalittoral sand. Because the fishing effort is aggregated in this habitat (90% of effort corresponding to ~30% of the area), the reduction of 10% of the effort corresponds to the exclusion of over ~50% of the original fished area with a limited improvement in the impact indicators (~1% in PD method, ~23% in L1 method). However such scenario still provides over ~80% of landing and values of the original amounts.

For the second most extensive habitat by area, offshore circalittoral mud, the reduction of 10% of the effort corresponds to a smaller portion of fished area lost (~40%) as the fishery was not as much aggregated, and to a larger improvement in the impact indicators (~1% PD model, ~29% L1 method) with comparable decrease in landing and value (less than 20%).

MSFD habitat - 1

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.05	0.54	11.68	100.00	100.00
5	0.05	0.40	53.70	90.95	94.28
10	0.04	0.31	65.43	83.24	89.33
15	0.04	0.26	72.51	75.71	83.87
20	0.04	0.21	77.66	68.52	78.54
30	0.03	0.15	84.63	55.82	65.20
40	0.03	0.10	89.44	43.77	55.58
60	0.01	0.04	95.46	22.95	28.61
80	0.01	0.01	98.58	7.00	6.41
99	0.00	0.00	99.97	0.08	0.03

MSFD habitat - 2

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.12	0.82	0.75	100.00	100.00
5	0.12	0.64	29.20	91.90	95.77
10	0.11	0.53	41.68	84.28	90.93
15	0.10	0.46	50.63	77.25	86.71
20	0.09	0.39	58.08	70.16	82.20
30	0.08	0.28	70.03	57.18	72.48
40	0.07	0.20	79.03	45.45	62.48
60	0.03	0.08	91.47	24.03	40.99
80	0.01	0.03	97.50	7.40	17.02
99	0.00	0.00	99.98	0.10	0.25

MSFD habitat - 3

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.05	0.47	7.59	100.00	100.00
5	0.04	0.37	50.04	84.50	94.79
10	0.04	0.29	64.30	71.53	90.17
15	0.03	0.24	72.43	61.52	85.24
20	0.03	0.20	78.21	52.98	79.18
30	0.02	0.14	85.33	42.81	66.08
40	0.02	0.10	89.93	33.32	49.72
60	0.01	0.04	95.76	18.54	26.68
80	0.00	0.01	98.81	7.20	7.49
99	0.00	0.00	100.00	0.10	0.03

MSFD habitat - 4

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.49	1.00	0.00	100.00	100.00
5	0.45	0.93	7.44	93.59	95.00
10	0.43	0.86	15.41	88.40	89.50
15	0.40	0.77	24.22	85.17	82.27
20	0.37	0.71	30.49	79.82	76.52
30	0.31	0.57	45.83	70.88	64.02
40	0.26	0.42	60.55	61.07	52.17
60	0.16	0.25	76.34	40.46	34.82
80	0.07	0.11	91.42	15.51	17.09
99	0.01	0.03	100.00	0.78	5.68

Overview all MSFD habitats

Fishing effort consequences, as a % relative to total swept area, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral sand	164.94	0.0	0.0	0.1	0.6	1.8	4.0	7.3	13.0	22.9	41.5
Offshore circalittoral mud	62.21	0.1	0.7	2.5	5.3	9.2	14.6	21.4	30.0	41.3	57.1
Offshore circalittoral coarse sediment	25.27	0.0	<0.1	0.3	1.2	2.7	5.0	8.2	13.4	22.1	40.3
Upper bathyal sediment	0.31	3.6	6.8	12.8	20.1	26.5	33.9	40.9	51.0	66.2	82.8
Offshore circalittoral mixed sediment	1.44	<0.1	0.2	1.0	1.9	3.5	7.9	13.8	22.0	37.8	62.2
Circalittoral sand	1.34	0.0	0.0	0.0	0.1	0.3	0.9	2.0	9.4	20.9	50.8
Circalittoral coarse sediment	0.72	0.0	<0.1	0.3	1.1	4.1	6.6	13.3	23.1	41.0	62.3
Circalittoral mud	0.75	0.0	0.0	<0.1	0.6	1.3	3.7	8.6	21.0	36.1	66.1
Unknown	0.42	0.0	0.0	0.0	0.0	0.1	0.5	1.8	5.5	15.9	48.6
Offshore circalittoral rock and biogenic reef	0.31	<0.1	0.3	1.3	3.1	6.0	10.2	13.4	19.7	30.7	53.2
Circalittoral rock and biogenic reef	0.52	0.0	0.0	<0.1	1.1	3.2	6.4	12.2	17.3	30.9	45.8
Circalittoral mixed sediment	0.17	0.0	0.0	0.0	0.0	0.8	1.7	6.6	12.9	28.2	60.8
Infralittoral rock and biogenic reef	0.15	0.0	0.0	0.0	0.2	0.9	3.3	6.3	14.1	23.5	44.3
Infralittoral sand	0.22	0.0	0.0	0.0	0.0	0.0	0.0	<0.1	3.3	10.1	50.4
Infralittoral coarse sediment	0.05	0.0	0.0	0.0	<0.1	0.6	1.6	8.1	17.5	39.9	58.2
Infralittoral mud	0.06	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.3	2.9
Infralittoral mixed sediment	0.02	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	19.1	19.1

Fishing value consequences, as a % relative to total value, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral sand	164.94	0.0	0.0	0.4	1.6	3.8	7.3	12.8	21.4	35.4	58.0
Offshore circalittoral mud	62.21	0.3	1.1	4.0	8.6	14.5	22.2	31.7	42.8	56.0	72.9
Offshore circalittoral coarse sediment	25.27	0.0	<0.1	1.1	3.5	8.1	15.6	24.6	35.2	49.7	66.9
Upper bathyal sediment	0.31	4.7	8.7	12.6	20.3	27.9	32.3	40.9	53.2	65.9	91.3
Offshore circalittoral mixed sediment	1.44	0.2	0.6	2.5	4.0	6.2	12.8	22.8	32.9	51.6	71.3
Circalittoral sand	1.34	0.0	0.0	0.0	0.4	1.2	2.3	3.9	11.2	25.2	56.1
Circalittoral coarse sediment	0.72	0.0	<0.1	0.5	1.5	4.7	9.5	16.6	26.7	40.3	54.7
Circalittoral mud	0.75	0.0	0.0	<0.1	1.3	2.5	4.8	9.5	21.9	40.1	65.3
Unknown	0.42	0.0	0.0	0.0	0.0	0.3	1.0	3.9	13.0	23.3	55.7
Offshore circalittoral rock and biogenic reef	0.31	<0.1	0.3	1.6	2.7	4.7	7.8	10.0	16.5	26.4	75.4
Circalittoral rock and biogenic reef	0.52	0.0	0.0	<0.1	1.2	3.2	7.8	15.0	18.3	27.7	41.3
Circalittoral mixed sediment	0.17	0.0	0.0	0.0	0.0	1.5	2.8	6.7	13.6	25.8	50.1
Infralittoral rock and biogenic reef	0.15	0.0	0.0	0.0	0.3	1.0	4.0	7.0	11.7	21.5	36.3
Infralittoral sand	0.22	0.0	0.0	0.0	0.0	0.0	0.0	<0.1	3.8	9.4	45.1
Infralittoral coarse sediment	0.05	0.0	0.0	0.0	<0.1	0.5	2.3	8.6	17.5	34.3	56.1
Infralittoral mud	0.06	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.5	1.3
Infralittoral mixed sediment	0.02	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	35.0	35.0

Fishing weight consequences, as a % relative to total weight, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral sand	164.94	<0.1	<0.1	0.4	1.3	2.6	4.7	7.9	13.4	25.6	46.4
Offshore circalittoral mud	62.21	0.2	0.6	2.0	4.5	8.0	13.0	19.1	27.5	39.2	55.2
Offshore circalittoral coarse sediment	25.27	0.0	<0.1	0.5	1.5	3.1	5.2	8.1	13.3	23.1	50.4
Upper bathyal sediment	0.31	4.0	7.5	15.4	23.8	32.7	42.4	50.1	60.4	73.6	85.6
Offshore circalittoral mixed sediment	1.44	0.1	0.4	1.9	3.0	5.7	13.9	24.6	35.7	47.8	64.2
Circalittoral sand	1.34	0.0	0.0	0.0	0.4	1.1	2.0	3.7	11.9	36.3	65.5
Circalittoral coarse sediment	0.72	0.0	<0.1	0.8	2.1	6.3	15.7	24.0	36.0	50.9	64.9
Circalittoral mud	0.75	0.0	0.0	0.1	1.6	3.1	5.8	10.7	23.8	40.5	66.2
Unknown	0.42	0.0	0.0	0.0	0.0	0.2	0.8	2.5	11.2	19.6	46.5
Offshore circalittoral rock and biogenic reef	0.31	<0.1	0.3	1.5	2.3	3.9	6.4	8.0	13.0	25.1	83.6
Circalittoral rock and biogenic reef	0.52	0.0	0.0	<0.1	1.0	2.5	8.0	12.8	16.0	23.3	34.2
Circalittoral mixed sediment	0.17	0.0	0.0	0.0	0.0	1.8	3.3	7.9	14.7	26.3	54.4
Infralittoral rock and biogenic reef	0.15	0.0	0.0	0.0	0.2	0.8	2.4	4.5	7.3	15.0	29.2
Infralittoral sand	0.22	0.0	0.0	0.0	0.0	0.0	0.0	<0.1	3.7	8.4	49.0
Infralittoral coarse sediment	0.05	0.0	0.0	0.0	0.1	0.8	3.5	11.9	24.0	46.7	62.8
Infralittoral mud	0.06	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.5	1.1
Infralittoral mixed sediment	0.02	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	31.1	31.1

Kattegat

Summary

The physical disturbance pressures from mobile bottom-contacting fishing gears in the Kattegat is mostly homogenous in the depth zone 0-200m between 2013 and 2018. After excluding the area that cannot be fished because of shallow waters (0-10m) (39%) (I-5), the average fishing intensity is 1.17 y-1 (I-1). This consist of 61% of the grid cells (I-2), and 36% of the surface area (I-3) being fished on average per year (Table 1). The fishery has 90% of the pressure being aggregated in 26% of grid cells (I-4), but this has to be considered in light of the large portion of unavailable area for fishing.

The PD method shows an average decline in community biomass of 17% relative to carrying capacity across c-squares (I-6) of which 71% are calculated to have an impact lower than 20% (I-7). The L1 method shows an average impact of 0.40 across c-squares (I-6) of which 56% are calculated to have an impact lower than 20% (I-7), the lowest average score among the subdivisions of the Greater North Sea. Both indicators are influenced by the relevant portion of surface area where pressure data are not available.

Maps of spatial distribution of intensity, seafloor sensitivity and economic value and weight of fisheries landings are shown in Figure 1. Seafloor sensitivity is very high in most of the Kattegat as the community longevity is mainly above 6-8 years. Total landing and value are mostly homogeneously distributed across the fished c-squares.

Table 1

Table 1. Pressure and impact indicators for 2013-2018

Indicators	0 to 200 m	200 to 800 m	more than 800 m
Average intensity (I-1)	1.17	NA	NA
Proportion of area in fished cells (I-2)	0.61	NA	NA
Proportion of area fished per year (I-3)	0.36	NA	NA
Smallest prop. of area in fished cells with 90% of fishing effort (I-4)	0.26	NA	NA
Proportion of area in unfished cells (I-5)	0.39	NA	NA
Average PD impact (I-6)	0.17	NA	NA
Average L1 impact (I-6)	0.40	NA	NA
Proportion of area with PD impact < 0.2 (I-7)	0.71	NA	NA
Proportion of area with L1 impact < 0.2 (I-7)	0.56	NA	NA

Figure 1

Figure 1 Geographic distribution of surface abrasion, seabed sensitivity (community longevity) and total value and weight from mobile bottom-contacting gear. The maps of surface abrasion, value and weight show the average per year for 2013-2018

Pressure

The distribution of fishing intensity in Kattegat does not have a strong spatial variation with regards to the c-squares where fishing is recorded (Figure 2). Within the latter area, peak of intensity is displayed in the northern area, but SAR between 1 and 5 y-1 are the predominant.

The proportion of area subject to fishing pressure differs between broad-scale habitats. The dominant habitat by area is offshore circalittoral mud. This habitat is also the most intensely and extensively fished with a fishing intensity of 2.92 and 94% of the grid cells fished. The second broad-habitat type by swept area is offshore circalittoral sand with an average intensity of 0.64 and 82% grid cells fished.

Total fishing intensity shows an overall decreasing trend over time between 2013 and 2018 (Figure 3). There is a large drop in intensity in offshore circalittoral mud between 2010 and 2016, despite the proportion of area fished and the aggregation of fishing pressure in the habitat remained constant over time. The average trawling intensity is more variable over time than the proportion of area fished (Figure 3, compare left and middle panel). This shows that changes in intensity have not affected the spatial distribution of the footprint much.

Among the four most extensive habitats, the proportion of area subject to fishing pressure is mostly constant over time, with only a visible small decrease in offshore circalittoral sand area fished. Fishing pressure is aggregated, both at the regional level as well as at the level of the habitat because of the limitation in fishable extents imposed by shallow depths (Figure 3, right panel). The smallest proportion of habitat with 90% of effort is constant over time between 10-50% across habitats. The ‘core fishing grounds’ contribute most of the landings and value (Figure 4). In Kattegat however, landing and value are more distributed across c-squares, despite being already concentrated by depth limitations. Around 50% of the landing come from 20% of the overall Kattegat subdivisions, while more than 60% value correspond to such surface area percentage (Figure 4).

Figure 2

Figure 2 Surface abrasion, Swept Area Ratio, by mobile bottom-contacting gears (year-1), averaged for the 2013-2018 six-year cycle

Table 2

Table 2 Overview of pressure indicators of all mobile bottom-contacting gears per broad-scale habitat averaged for 2013-2018. I refers to the indicators in Table 1.

MSFD broad habitat type	Extent of habitat (1000 km2)	Number of grid cells	Landings 1000 tonnes	Value 106 euro	Swept area 1000 km2	Average intensity (I-1)	Prop. of area in fished grid cells (I-2)	Prop. of area fished per year (I-3)	Smallest prop. of area with 90% of fishing effort (I-4)
Offshore circalittoral mud	8.21	743	3.91	17.23	23.93	2.92	0.94	0.78	0.42
Offshore circalittoral sand	3.11	556	1.02	1.43	2.00	0.64	0.82	0.30	0.22
Offshore circalittoral mixed sediment	1.33	500	0.26	0.74	1.07	0.80	0.84	0.35	0.27
Circalittoral mud	0.73	266	0.39	0.91	1.04	1.42	0.68	0.55	0.10
Offshore circalittoral coarse sediment	0.59	335	0.17	0.34	0.52	0.88	0.79	0.35	0.27
Infralittoral sand	4.35	639	0.09	0.14	0.19	0.04	0.29	0.04	0.08
Circalittoral sand	0.43	345	0.06	0.09	0.13	0.30	0.57	0.16	0.12
Offshore circalittoral rock and biogenic reef	0.04	80	0.00	0.03	0.04	1.21	0.99	0.59	0.29
Circalittoral mixed sediment	0.51	279	0.01	0.02	0.04	0.08	0.46	0.05	0.16
Circalittoral coarse sediment	0.17	224	0.01	0.03	0.04	0.23	0.49	0.13	0.17
Infralittoral coarse sediment	0.20	222	0.02	0.03	0.03	0.15	0.46	0.09	0.12
Infralittoral mixed sediment	1.16	447	0.02	0.02	0.03	0.02	0.34	0.02	0.11
Circalittoral rock and biogenic reef	0.04	103	0.00	0.00	0.01	0.17	0.77	0.14	0.21
Infralittoral mud	0.76	237	0.00	0.00	0.01	0.01	0.07	0.01	0.05
Infralittoral rock and biogenic reef	0.06	118	0.00	0.00	0.00	0.06	0.62	0.06	0.19
Unknown	0.00	174	0.00	0.00	0.00	0.09	0.45	0.08	0.06

Figure 3

Figure 3. Time series of (a) mean fishing intensity (surface abrasion), (b) proportion of the surface area of the seafloor fished, (c) aggregation of fishing (proportion of the surface area with 90% of the fishing effort) by habitat. Results represent vessels over 15m (2009-2011) and vessels over 12m (2012-2018).

Figure 4

Figure 4. Cumulative proportion of the swept area, landings and value. Grid cells were sorted from highest to lowest fishing intensity and include non-fished cells. The results are for all mobile bottom-contacting gears based on averaged fishing data per c-square from 2013-2018.

Core fishing grounds

Core fishing grounds are defined as the c-squares with the 90% highest value of landings in the VMS data. Figure 5 shows the number of years c-squares are within the 90% highest value by métier. If fishing in a métier occurs in the same c-square every year with high value of landings, the rightmost bar in Figure 5 and 6 will be high, meaning that the c-square is within the 90% highest value of landings every year during the period 2013-2018. If a c-square is only within the 90% highest value in one year, it will end up in the bar at the left. Figure 6 shows the percentage area overlap between the 90% highest value per year and the reference fishing ground.

In Kattegat, three main MBCG are active. The core fishing grounds for otter trawl targeting crustaceans (OT_CRU) are very stable over time, with the highest spatial overlap and time stability. Oppositely, the core fishing grounds for otter trawl targeting small pelagic fish (OT_SPF) are very variable, with low percentage of overlap between years and variable landing value and area ratio over time. Otter trawl targeting demersal fish (OT_DMF) display an intermediate variability.

Figure 7 illustrates the relationship between area fished in percent and the cumulated value of landings, sorted from the c-squares with highest value fisheries. The curves are generally starting steeply, illustrating the concentration of the fisheries at fishing grounds and the curves are ending horizontally, illustrating the peripheral fisheries going on outside the main fishing grounds.

Figure 5

Figure 5. Number of years c-squares are within the 90% core fishing grounds by metier during the period 2013-2018

Figure 6

Figure 6. Percentage area overlap between the 90% highest value per year and the reference core fishing ground

Figure 7

Figure 7. Percent area fished vs. landings value (euro) by métier, coloured by year

Fishing by métier

Intensity, weight and value of landings are estimated for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers (Table 3).

The métier with the highest landings and value per area fished is the otter trawl for small pelagic fish (OT_SPF). Otter trawl targeting crustaceans (OT_CRU) has the highest area swept but the least landing per area value.

Table 3

Table 3. Overview of area fished (sum of swept area), landings and value for the different metiers. Area fished in 1000 km², weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Area swept (1000 km2)	0	22.82	5.29	0	0.30	0.76	0.05	<0.005	<0.005	0
Landings (1000 tonnes)	0	2.50	1.80	0	1.49	0.22	<0.005	<0.005	<0.005	0
Value (10^6 euro)	0	17.73	2.61	0	0.37	0.35	<0.005	<0.005	<0.005	0
Landings (1000 tonnes)/Area swept (1000 km2)	NaN	0.11	0.34	NaN	5.04	0.29	<0.005	0.66	0.4	NaN
Value (10^6 euro)/Area swept (1000 km2)	NaN	0.78	0.49	NaN	1.24	0.46	<0.005	3.37	1.02	NaN

Impact

Both the impact of mobile bottom-contacting fishing from the PD method and the L1 method have a strong spatial variability due to large unfished areas. In the fished areas, the impact scores are both extensive and high in value, especially in the northern area of Kattegat (Figure 8).

The impact scores are largely constant over time (Figure 9, left panel). Impact varies between habitats (Figure 8 shows the four most extensive habitat types). Of these four most extensive habitat types, impact is highest in offshore circalittoral mud. Offshore circalittoral mud also has the least percentage of c-square where impacts are kept lower than 0.2 (below 25%).

Table 4 shows impact per métier relative to weight and value of landings. In this analysis, the different métiers are assessed for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers. As such this estimates the maximum impact compared to the untrawled situation and the impact estimated assuming all other métiers to have impacted the habitat will be less than this. Active métier seems to all have high impact (PD and L1) relative to the value and landings. The otter trawl for small pelagic fish (OT_SPF) has the lowest impact per value and landings especially with the regards to the biomass impact indicator (Table 3).

Métiers differ in their habitat association and impact on each habitat type (Figure 10). In Kattegat, fishing impact is mostly located in the offshore circalittoral mud habitat due to otter trawl métiers targeting crustaceans and small pelagic fish (OT_CRU and OT_SPF). The second most impacted habitat by the above-mentioned métier is offshore circalittoral mixed sediments.

Figure 8

Figure 8. Impact of mobile bottom-contacting gears averaged for the 2013-2018 six-year cycle for the PD and L1 method.

Figure 9

Figure 9. The mean impact of mobile bottom-contacting gears in all combined MSFD habitats and the four most extensive habitat types between 2009 and 2018 (left). The proportion of the fished area with an impact of less than 0.2 (right)

Table 4

Table 4. Overview of impact per metier relative to weight and value of landings estimated for the grid cells fished (SAR >0) with these métiers only. Weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Landings (1000 tonnes)/PD impact	NA	0.010	0.088	NA	2.371	0.186	0.001	0.117	0.040	NA
Value (10^6 euro)/PD impact	NA	0.074	0.129	NA	0.582	0.295	0.004	0.600	0.102	NA
Landings (1000 tonnes)/L1 impact	NA	0.005	0.004	NA	0.029	0.016	0.000	0.023	0.003	NA
Value (10^6 euro)/L1 impact	NA	0.034	0.006	NA	0.007	0.026	0.000	0.116	0.008	NA

Figure 10

Figure 10. PD impact (upper panel) and L1 impact (lower panel) of selected gear groupings on the most extensive MSFD habitat types. Impact is estimated in isolation of the other gear groupings. Note the different scales on the Y-axis.

Management scenarios

The figures and tables below show one implementation of multi-purpose habitat management through reductions in effort and spatial closures for the four most extensive MSFD habitat types. They show the changes in average impact (PD, L1), unfished area and fisheries values of landings based on a static assessment of effort removal.

The analysis is based on the progressive removal of 5 to 99% of all MBCG fishing effort, starting from the c-squares with the lowest effort (corrected for the areal extent of the MSFD habitat within each c-square). Blue dots show the current situation and are used as reference. The % of unfished area in the reference is only based on grid cells that are unfished. Average PD and L1 impacts are a weighted average and consider the areal extent of each MSFD habitat type within a grid cell.

Note that the fraction of grid cells above/below a certain impact threshold initially remains the same (not shown) as the removal of effort starts from the c-squares with the lowest effort that typically have low impact.

Most of the bottom-contacting fishing activity in Kattegat is taking place within the offshore circalittoral mud habitat. When effort is reduced by 20%, both average impact scores show a net improvement with ~ 30% improvement for the L1 indicator. However, that corresponds a 20-40% reduction in value and landings.

MSFD habitat - 1

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.43	0.82	6.03	100.00	100.00
5	0.41	0.67	33.29	94.68	87.76
10	0.39	0.60	39.89	89.76	82.18
15	0.36	0.54	45.63	84.27	73.84
20	0.34	0.49	50.93	78.65	67.39
30	0.29	0.40	60.20	67.54	56.62
40	0.24	0.32	67.90	56.15	45.61
60	0.15	0.19	81.13	35.88	28.94
80	0.07	0.08	92.17	16.39	12.95
99	0.00	0.00	99.80	1.06	0.94

MSFD habitat - 2

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.08	0.39	17.61	100.00	100.00
5	0.07	0.32	63.63	94.87	92.84
10	0.07	0.28	70.87	88.22	84.79
15	0.06	0.25	74.88	82.44	77.33
20	0.06	0.21	78.53	77.30	70.72
30	0.05	0.17	83.29	67.14	63.34
40	0.04	0.13	87.48	56.82	51.03
60	0.02	0.06	94.36	35.35	32.84
80	0.01	0.01	98.86	15.62	14.48
99	0.00	0.00	100.00	7.28	7.13

MSFD habitat - 3

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.13	0.44	16.49	100.00	100.00
5	0.12	0.38	55.09	94.97	86.77
10	0.12	0.34	60.92	90.38	76.50
15	0.11	0.31	65.89	86.05	71.65
20	0.11	0.27	72.30	81.87	67.86
30	0.09	0.20	80.01	69.96	38.98
40	0.08	0.17	83.51	60.74	28.98
60	0.05	0.11	89.22	41.48	20.19
80	0.03	0.06	94.74	21.84	9.23
99	0.00	0.00	100.00	3.18	1.27

MSFD habitat - 4

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.18	0.58	31.75	100.00	100.00
5	0.17	0.51	47.02	95.49	95.87
10	0.17	0.45	56.82	91.19	79.36
15	0.16	0.41	60.11	86.60	76.02
20	0.15	0.39	61.89	82.12	73.01
30	0.13	0.32	70.08	70.89	58.29
40	0.11	0.26	76.18	62.10	51.25
60	0.07	0.15	86.77	41.09	35.32
80	0.02	0.06	95.75	18.35	20.56
99	0.01	0.02	100.00	6.09	8.62

Overview all MSFD habitats

Fishing effort consequences, as a % relative to total swept area, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral mud	8.21	0.0	<0.1	0.4	3.2	10.2	19.3	30.0	43.2	58.1	76.1
Offshore circalittoral sand	3.11	0.0	0.0	<0.1	0.2	0.5	1.5	3.7	8.8	23.8	48.1
Offshore circalittoral mixed sediment	1.33	0.0	0.0	<0.1	0.2	1.0	2.9	9.5	18.1	30.3	63.8
Circalittoral mud	0.73	0.0	0.0	0.0	0.0	0.6	7.0	15.1	31.4	49.4	71.1
Offshore circalittoral coarse sediment	0.59	0.0	0.0	0.0	0.2	0.8	1.6	7.7	14.9	36.9	62.8
Infralittoral sand	4.35	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.3	6.0
Circalittoral sand	0.43	0.0	0.0	0.0	0.0	0.0	0.2	1.2	4.4	10.2	40.4
Offshore circalittoral rock and biogenic reef	0.04	<0.1	0.1	1.2	4.8	8.0	13.7	25.1	43.9	54.9	83.3
Circalittoral mixed sediment	0.51	0.0	0.0	0.0	0.0	0.0	0.0	0.9	2.6	6.3	16.2
Circalittoral coarse sediment	0.17	0.0	0.0	0.0	0.0	0.0	0.0	0.4	2.0	5.3	19.1
Infralittoral coarse sediment	0.2	0.0	0.0	0.0	0.0	0.0	0.0	0.3	1.3	5.3	18.2
Infralittoral mixed sediment	1.16	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.5	6.1	20.9
Circalittoral rock and biogenic reef	0.04	0.0	0.0	0.0	0.2	1.1	3.0	5.3	13.5	30.1	67.3
Infralittoral mud	0.76	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
Infralittoral rock and biogenic reef	0.06	0.0	0.0	0.0	0.0	0.2	0.8	4.0	7.2	18.3	38.6
Unknown	0	0.0	0.0	0.0	0.0	0.0	0.0	0.4	1.6	3.3	42.7

Fishing value consequences, as a % relative to total value, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral mud	8.21	0.0	<0.1	0.4	3.5	10.6	20.7	32.5	47.4	62.3	80.0
Offshore circalittoral sand	3.11	0.0	0.0	<0.1	0.1	0.4	1.3	3.8	9.4	26.6	52.4
Offshore circalittoral mixed sediment	1.33	0.0	0.0	<0.1	0.2	0.9	2.7	9.4	16.7	30.5	62.5
Circalittoral mud	0.73	0.0	0.0	0.0	0.0	0.5	6.2	14.9	31.7	50.3	75.9
Offshore circalittoral coarse sediment	0.59	0.0	0.0	0.0	0.2	0.8	1.7	9.2	17.2	38.7	62.5
Infralittoral sand	4.35	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.2	5.3
Circalittoral sand	0.43	0.0	0.0	0.0	0.0	0.0	0.3	1.2	5.0	11.7	53.2
Offshore circalittoral rock and biogenic reef	0.04	<0.1	0.2	1.1	4.4	7.4	12.9	23.6	42.0	52.2	81.8
Circalittoral mixed sediment	0.51	0.0	0.0	0.0	0.0	0.0	0.0	1.2	3.0	7.0	16.2
Circalittoral coarse sediment	0.17	0.0	0.0	0.0	0.0	0.0	0.0	0.5	1.8	4.5	16.6
Infralittoral coarse sediment	0.2	0.0	0.0	0.0	0.0	0.0	0.0	0.2	0.8	4.1	13.9
Infralittoral mixed sediment	1.16	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.3	5.4	21.2
Circalittoral rock and biogenic reef	0.04	0.0	0.0	0.0	0.3	1.3	3.5	6.1	14.6	27.7	65.0
Infralittoral mud	0.76	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
Infralittoral rock and biogenic reef	0.06	0.0	0.0	0.0	0.0	0.1	0.9	4.0	8.1	20.4	37.1
Unknown	0	0.0	0.0	0.0	0.0	0.0	0.0	0.6	1.8	3.3	53.1

Fishing weight consequences, as a % relative to total weight, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral mud	8.21	0.0	<0.1	1.1	10.5	19.4	32.0	43.4	58.0	69.6	83.6
Offshore circalittoral sand	3.11	0.0	0.0	<0.1	0.3	0.6	2.1	6.0	13.7	33.1	55.6
Offshore circalittoral mixed sediment	1.33	0.0	0.0	0.2	0.9	2.7	8.4	23.4	31.6	61.2	81.5
Circalittoral mud	0.73	0.0	0.0	0.0	0.0	0.5	6.5	24.6	42.8	58.9	73.3
Offshore circalittoral coarse sediment	0.59	0.0	0.0	0.0	0.6	2.1	4.7	16.1	31.3	40.9	61.8
Infralittoral sand	4.35	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.3	6.4
Circalittoral sand	0.43	0.0	0.0	0.0	0.0	0.0	0.2	1.0	5.5	16.7	70.0
Offshore circalittoral rock and biogenic reef	0.04	<0.1	0.2	1.4	5.9	10.0	17.5	29.0	47.1	56.3	84.2
Circalittoral mixed sediment	0.51	0.0	0.0	0.0	0.0	0.0	0.0	6.6	11.0	22.3	43.8
Circalittoral coarse sediment	0.17	0.0	0.0	0.0	0.0	0.0	0.0	0.5	4.1	5.8	25.7
Infralittoral coarse sediment	0.2	0.0	0.0	0.0	0.0	0.0	0.0	0.2	1.2	5.1	16.2
Infralittoral mixed sediment	1.16	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.9	4.0	24.0
Circalittoral rock and biogenic reef	0.04	0.0	0.0	0.0	0.4	1.7	4.0	8.8	18.1	32.1	69.2
Infralittoral mud	0.76	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
Infralittoral rock and biogenic reef	0.06	0.0	0.0	0.0	0.0	0.3	1.4	4.3	8.2	23.0	45.5
Unknown	0	0.0	0.0	0.0	0.0	0.0	0.0	0.9	2.3	4.5	74.8

Southern North Sea

Summary

The physical disturbance pressures from mobile bottom-contacting fishing gears varies spatially across the Southern North Sea subdivision with an average swept area ratio of 1.6 y-1. For the period 2013-2018, 96% of the grid cells (I-2), and 71% of the surface area (I-3) were fished on average per year in the depth zone 0-200m (Table 1). Fishing in the Southern North Sea is the least aggregated among the Greater North Sea subdivisions with 90% of the pressure occurring in 55% of grid cells (I-4). Fishing is not occurring in 4% of grid cells.

The PD method shows an average decline in community biomass of 13% relative to carrying capacity across c-squares (I-6). Most c-squares, 78% (I-7), have an impact score less than 20%. The L1 method shows a larger impact on a larger portion of c-squares, with an average score of 0.77 (I-6) and only 13% (I-7) of the c-squares having a score lower than 20% (I-7).

Maps of spatial distribution of intensity, seafloor sensitivity and economic value and weight of fisheries landings are shown in Figure 1. Note that for the Southern North Sea, benthic species median longevity gradually increases with latitude.

All pressure and impact estimates are for areas < 200 meter depth as there is no longevity prediction for deeper regions.

Table 1

Table 1. Pressure and impact indicators for 2013-2018

Indicators	0 to 200 m	200 to 800 m	more than 800 m
Average intensity (I-1)	1.60	NA	NA
Proportion of area in fished cells (I-2)	0.96	NA	NA
Proportion of area fished per year (I-3)	0.71	NA	NA
Smallest prop. of area in fished cells with 90% of fishing effort (I-4)	0.55	NA	NA
Proportion of area in unfished cells (I-5)	0.04	NA	NA
Average PD impact (I-6)	0.13	NA	NA
Average L1 impact (I-6)	0.77	NA	NA
Proportion of area with PD impact < 0.2 (I-7)	0.78	NA	NA
Proportion of area with L1 impact < 0.2 (I-7)	0.13	NA	NA

Figure 1

Figure 1 Geographic distribution of surface abrasion, seabed sensitivity (community longevity) and total value and weight from mobile bottom-contacting gear. The maps of surface abrasion, value and weight show the average per year for 2013-2018

Pressure

The distribution of fishing intensity in the Southern North Sea shows the most homogenous pattern among the Greater North Sea subdivisions, despite a certain level of spatial variation can still be found (Figure 2). Areas of higher intensity occur along the Belgian and Dutch coasts and few locations offshore.

The proportion of area subject to fishing pressure differs between broad-scale habitats and is highest in offshore circalittoral mud and offshore circalittoral rock and biogenic reef where 100% of the grid cells are fished. They are followed by offshore circalittoral sand and mixed sediments with 99% of the grid cells being fished. (Table 2). Fishing intensity is highest in offshore circalittoral mud (average intensity = 2.43 y-1) and circalittoral mud (average intensity = 2.28 y-1).

Figure 3 shows the trends of fishing intensity, fished area and core-fishing ground coverage over time within the four most widely distributed broad-scale habitat type of the Southern North Sea. Total fishing intensity shows a decreasing trend from 2013 to 2018 for all broad-scale habitat except for offshore circalittoral mud (Figure 3, left panel). The decrease seems less pronounced for the proportion of area fished over time, thus only partially reflecting the decrease in intensity (Figure 3, middle panel).

Fishing pressure remains aggregated to a largely constant extent over time, showing a similar pattern within each broad-scale habitat type (Figure 3, right panel). The smallest proportion of habitat with 90% of effort varies between a minimum of 20% and a maximum of 50%. These core-fishing grounds contribute to most of the landings and value. More than 60% of the landings are trawled within 20% of the total surface area, while the curve is less steep for the cumulative value (Figure 4).

Figure 2

Figure 2 Surface abrasion, Swept Area Ratio, by mobile bottom-contacting gears (year-1), averaged for the 2013-2018 six-year cycle

Table 2

Table 2 Overview of pressure indicators of all mobile bottom-contacting gears per broad-scale habitat averaged for 2013-2018. I refers to the indicators in Table 1.

MSFD broad habitat type	Extent of habitat (1000 km2)	Number of grid cells	Landings 1000 tonnes	Value 106 euro	Swept area 1000 km2	Average intensity (I-1)	Prop. of area in fished grid cells (I-2)	Prop. of area fished per year (I-3)	Smallest prop. of area with 90% of fishing effort (I-4)
Offshore circalittoral sand	69.03	6102	98.78	120.04	96.90	1.40	0.99	0.75	0.50
Circalittoral sand	58.53	5888	130.29	124.87	90.92	1.55	0.98	0.71	0.42
Offshore circalittoral mud	29.48	2612	43.09	48.98	71.69	2.43	1.00	0.91	0.49
Offshore circalittoral coarse sediment	14.15	2175	10.57	25.52	24.34	1.72	0.93	0.56	0.25
Infralittoral sand	6.43	1391	16.04	26.85	14.56	2.26	0.97	0.81	0.35
Circalittoral coarse sediment	16.18	2899	16.30	14.03	11.34	0.70	0.77	0.39	0.29
Unknown	2.20	506	3.58	12.78	7.97	3.63	0.89	0.69	0.17
Circalittoral mud	3.46	851	16.83	11.62	7.90	2.28	0.98	0.74	0.26
Offshore circalittoral mixed sediment	1.90	487	1.45	2.43	2.99	1.58	0.99	0.71	0.29
Circalittoral mixed sediment	3.07	721	2.04	2.41	1.97	0.64	0.90	0.45	0.32
Infralittoral coarse sediment	1.11	427	1.92	2.46	1.78	1.61	0.96	0.80	0.20
Infralittoral mud	0.29	356	0.34	1.09	0.50	1.71	0.86	0.55	0.21
Infralittoral mixed sediment	0.03	54	0.01	0.02	0.01	0.31	0.80	0.12	0.19
Offshore circalittoral rock and biogenic reef	0.00	10	0.00	0.01	0.01	1.49	1.00	0.50	NA
Infralittoral rock and biogenic reef	0.00	6	0.00	0.00	0.00	0.02	0.37	0.02	NA
Circalittoral rock and biogenic reef	0.00	5	0.00	0.00	0.00	0.04	0.73	0.04	NA

Figure 3

Figure 3. Time series of (a) mean fishing intensity (surface abrasion), (b) proportion of the surface area of the seafloor fished, (c) aggregation of fishing (proportion of the surface area with 90% of the fishing effort) by habitat. Results represent vessels over 15m (2009-2011) and vessels over 12m (2012-2018).

Figure 4

Figure 4. Cumulative proportion of the swept area, landings and value. Grid cells were sorted from highest to lowest fishing intensity and include non-fished cells. The results are for all mobile bottom-contacting gears based on averaged fishing data per c-square from 2013-2018.

Core fishing grounds

Core fishing grounds are defined as the c-squares with the 90% highest value of landings in the VMS data. Figure 5 shows the number of years c-squares are within the 90% highest value by métier. If fishing in a métier occurs in the same c-square every year with high value of landings, the rightmost bar in Figure 5 and 6 will be high, meaning that the c-square is within the 90% highest value of landings every year during the period 2013-2018. If a c-square is only within the 90% highest value in one year, it will end up in the bar at the left. Figure 6 shows the percentage area overlap between the 90% highest value per year and the reference fishing ground. Results shows that in the Southern North Sea the otter trawl métiers targeting small pelagic fish and demersal fish (OT_SPF, OT_DMF) together with the seine (SSC_DMF, SDN_DMF) have the highest variation in space, while beam trawl métiers are the most consistent in time.

Figure 7 illustrates the relationship between area fished in percent and the cumulated value of landings, sorted from the c-squares with highest value fisheries. The curves are generally starting steeply, illustrating the concentration of the fisheries at fishing grounds and the curves are ending horizontally, illustrating the peripheral fisheries going on outside the main fishing grounds. The métiers targeting demersal fish species and the otter trawl mixed fishery (OT_MIX) are the ones showing the most variation among years.

Figure 5

Figure 5. Number of years c-squares are within the 90% core fishing grounds by metier during the period 2013-2018

Figure 6

Figure 6. Percentage area overlap between the 90% highest value per year and the reference core fishing ground

Figure 7

Figure 7. Percent area fished vs. landings value (euro) by métier, coloured by year

Fishing by métier

Intensity, weight and value of landings are estimated for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers (Table 3).

The métiers with the highest value per area swept in the Southern North Sea are the beam trawl fishery for whelks, snails and scallop (TBB_MOL) and the dredges for mussel and scallop (DRB_MOL) despite a very small surface area was swept by both. The métiers targeting demersal fish species (OT_DMF, SDN_DMF and SSC_DMF) have the lowest value per area swept, although they are two of the most highest value métiers together with otter trawls targeting crustaceans (OT_CRU).

Table 3

Table 3. Overview of area fished (sum of swept area), landings and value for the different metiers. Area fished in 1000 km², weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Area swept (1000 km2)	0.25	50.90	86.55	0.91	3.65	10.30	40.84	55.02	92.58	0.02
Landings (1000 tonnes)	12.91	4.17	194.77	0.43	49.54	1.00	3.72	26.08	56.81	1.60
Value (10^6 euro)	19.61	16.97	53.50	1.18	10.38	2.31	6.45	94.50	213.45	2.31
Landings (1000 tonnes)/Area swept (1000 km2)	52.51	0.08	2.25	0.47	13.56	0.10	0.09	0.47	0.61	106.17
Value (10^6 euro)/Area swept (1000 km2)	79.79	0.33	0.62	1.30	2.84	0.22	0.16	1.72	2.31	153.46

Impact

The impact of mobile bottom-contacting fishing from the PD method shows the areas of highest fishing impact within the Belgian waters, along the Dutch coast and in the Dutch and German offshore waters (Figure 8, left). Majority of the Southern North Sea displays an impact from the L1 method above 0.8, with lower impacted area corresponding to least fished areas (Figure 8, right).

The impact scores are largely constant over time (Figure 9, left panel), with an overall slight increase in surface area with impact score lower than 0.2 for both indicators. However, impact varies between habitats (Figure 8 shows the four most extensive habitat types). Of these four habitat types, impact is highest in offshore circalittoral mud and lowest in circalittoral coarse sediments (the latter being fished with an overall average of 0.70 times y-1). Between 50-90% of each habitat type has a PD impact score <0.2, whereas only 10-50% of each habitat type has an L1 impact score <0.2.

Table 4 shows impact per métier relative to weight and value of landings. In this analysis, the different métiers are assessed for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers. As such this estimates the maximum impact compared to the untrawled situation and the impact estimated assuming all other métiers to have impacted the habitat will be less than this. The métiers with the highest impact (PD and L1) relative to the value and landings are the seines fisheries for demersal fish species (SDN_DMF and SSC_DMF) and the otter trawl fishery for crustaceans (OT_CRU) with a ratio between 0 and 0.01 for both metrics. The métiers targeting mollusks seem to be the least impactful but again the area swept was very small (Table 3).

Each métier shows a different impact among the four most distributed broad-scale habitat types (Figure 10). Offshore circalittoral mud is mostly impacted by the otter trawl fishery (OT_CRU and OT_DMF) followed by beam trawl fishery targeting demersal fish. Offshore circalittoral sand is the second most impacted habitat, mainly due to métiers targeting demersal fish. The two impact indicators are typically showing similar qualitative patterns but differ in scores.

Figure 8

Figure 8. Impact of mobile bottom-contacting gears averaged for the 2013-2018 six-year cycle for the PD and L1 method.

Figure 9

Figure 9. The mean impact of mobile bottom-contacting gears in all combined MSFD habitats and the four most extensive habitat types between 2009 and 2018 (left). The proportion of the fished area with an impact of less than 0.2 (right)

Table 4

Table 4. Overview of impact per metier relative to weight and value of landings estimated for the grid cells fished (SAR >0) with these métiers only. Weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Landings (1000 tonnes)/PD impact	4.079	0.013	1.041	0.105	13.077	0.123	0.085	0.136	0.070	20.381
Value (10^6 euro)/PD impact	6.199	0.053	0.286	0.290	2.742	0.285	0.148	0.493	0.262	29.458
Landings (1000 tonnes)/L1 impact	0.895	0.003	0.047	0.012	0.139	0.003	0.002	0.022	0.011	1.645
Value (10^6 euro)/L1 impact	1.361	0.011	0.013	0.032	0.029	0.006	0.004	0.081	0.042	2.377

Figure 10

Figure 10. PD impact (upper panel) and L1 impact (lower panel) of selected gear groupings on the most extensive MSFD habitat types. Impact is estimated in isolation of the other gear groupings. Note the different scales on the Y-axis.

Management scenarios

The figures and tables below show one implementation of multi-purpose habitat management through reductions in effort and spatial closures for the four most extensive MSFD habitat types. They show the changes in average impact (PD, L1), unfished area and fisheries values of landings based on a static assessment of effort removal.

The analysis is based on the progressive removal of 5 to 99% of all MBCG fishing effort, starting from the c-squares with the lowest effort (corrected for the areal extent of the MSFD habitat within each c-square). Blue dots show the current situation and are used as reference. The % of unfished area in the reference is only based on grid cells that are unfished. Average PD and L1 impacts are a weighted average and consider the areal extent of each MSFD habitat type within a grid cell.

Note that the fraction of grid cells above/below a certain impact threshold initially remains the same (not shown) as the removal of effort starts from the c-squares with the lowest effort that typically have low impact.

The offshore circalittoral mud habitat, which has the highest fishing intensity and the highest impacts, shows the greatest decline in average impact indicators within the first 20% reduction of fishing effort, however consisting in a ~50% increase in unfished areas. Offshore circalittoral sand, displays a similar reduction pattern.

MSFD habitat - 1

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.13	0.83	0.60	100.00	100.00
5	0.12	0.73	22.33	94.61	93.67
10	0.11	0.64	33.40	89.42	87.87
15	0.11	0.56	42.00	84.72	82.80
20	0.10	0.49	49.63	79.91	78.28
30	0.09	0.37	62.10	69.83	68.84
40	0.07	0.28	72.25	58.39	60.92
60	0.04	0.12	87.60	33.30	44.81
80	0.01	0.04	96.46	11.78	26.72
99	0.00	0.00	99.96	0.64	2.75

MSFD habitat - 2

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.12	0.76	1.78	100.00	100.00
5	0.11	0.66	28.28	94.98	96.65
10	0.10	0.57	39.57	89.86	93.27
15	0.10	0.50	47.80	83.19	89.32
20	0.09	0.43	55.25	78.95	86.67
30	0.08	0.32	67.12	70.69	80.91
40	0.06	0.23	76.53	62.60	75.67
60	0.04	0.11	89.15	44.84	62.10
80	0.02	0.04	96.33	24.04	13.05
99	0.00	0.00	99.90	2.02	0.47

MSFD habitat - 3

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.21	0.95	0.12	100.00	100.00
5	0.20	0.81	16.70	90.98	86.93
10	0.19	0.69	30.07	82.96	73.98
15	0.18	0.59	40.90	75.68	64.04
20	0.17	0.50	49.41	68.76	56.19
30	0.15	0.37	62.75	55.93	42.19
40	0.12	0.27	73.27	43.92	31.44
60	0.08	0.13	86.59	26.73	14.91
80	0.04	0.05	94.80	12.68	6.38
99	0.00	0.00	99.88	0.84	0.37

MSFD habitat - 4

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.12	0.62	7.22	100.00	100.00
5	0.11	0.51	44.65	92.97	89.33
10	0.10	0.43	55.66	86.20	79.05
15	0.09	0.36	63.40	79.68	71.95
20	0.09	0.31	68.92	73.57	62.47
30	0.07	0.22	77.98	60.13	47.12
40	0.05	0.16	84.01	46.65	34.75
60	0.03	0.07	93.02	25.54	19.32
80	0.01	0.02	97.93	11.52	9.46
99	0.00	0.00	100.00	0.61	0.63

Overview all MSFD habitats

Fishing effort consequences, as a % relative to total swept area, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral sand	69.03	0.3	1.2	4.2	8.4	13.7	20.3	28.2	37.5	49.0	64.2
Circalittoral sand	58.53	<0.1	0.4	2.4	5.7	10.3	16.4	23.7	32.7	44.6	61.8
Offshore circalittoral mud	29.48	1.3	2.8	6.1	10.0	14.5	20.4	27.7	36.7	48.9	67.4
Offshore circalittoral coarse sediment	14.15	0.0	<0.1	0.3	1.3	3.6	7.1	12.9	21.0	33.5	51.9
Infralittoral sand	6.43	<0.1	0.3	3.0	8.3	15.6	23.5	35.0	46.0	58.8	75.3
Circalittoral coarse sediment	16.18	0.0	0.0	0.0	0.1	1.0	4.3	10.8	20.9	34.6	55.4
Unknown	2.2	0.0	0.0	0.2	1.3	3.7	8.7	14.5	27.7	46.6	68.5
Circalittoral mud	3.46	0.1	0.9	3.3	6.6	11.6	16.9	23.1	31.6	43.6	65.1
Offshore circalittoral mixed sediment	1.9	<0.1	0.5	3.4	7.6	13.2	20.1	26.8	36.7	50.5	65.7
Circalittoral mixed sediment	3.07	0.0	0.0	0.2	1.7	6.6	11.9	22.2	31.5	46.7	66.7
Infralittoral coarse sediment	1.11	<0.1	0.2	1.6	11.8	23.3	31.7	44.1	55.1	68.3	81.2
Infralittoral mud	0.29	0.0	0.0	<0.1	0.5	3.2	7.8	16.8	33.9	54.0	76.2
Infralittoral mixed sediment	0.03	0.0	0.0	<0.1	1.3	3.7	4.3	6.3	7.3	13.5	18.1
Offshore circalittoral rock and biogenic reef	0	0.4	0.7	1.3	1.3	3.7	17.7	17.7	17.7	100.0	100.0
Infralittoral rock and biogenic reef	0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	41.8	41.8	100.0
Circalittoral rock and biogenic reef	0	0.0	0.0	0.0	41.4	100.0	100.0	100.0	100.0	100.0	100.0

Fishing value consequences, as a % relative to total value, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral sand	69.03	0.4	1.3	4.6	8.8	14.1	20.3	28.1	38.7	52.9	71.7
Circalittoral sand	58.53	<0.1	0.5	2.4	5.6	10.4	18.0	24.0	31.6	41.2	56.8
Offshore circalittoral mud	29.48	2.6	5.4	10.8	17.0	23.7	31.8	41.3	52.4	64.2	78.8
Offshore circalittoral coarse sediment	14.15	<0.1	<0.1	0.4	1.8	4.8	10.1	17.9	28.0	44.6	66.3
Infralittoral sand	6.43	<0.1	0.4	4.4	9.7	23.0	39.6	49.7	58.1	67.5	79.9
Circalittoral coarse sediment	16.18	0.0	0.0	<0.1	0.2	1.0	4.6	10.7	32.0	43.4	60.3
Unknown	2.2	0.0	0.0	0.3	2.0	4.4	10.4	17.2	32.9	50.7	68.0
Circalittoral mud	3.46	0.2	1.1	4.1	8.5	14.8	20.4	26.8	37.9	51.9	73.6
Offshore circalittoral mixed sediment	1.9	0.2	1.1	6.0	12.5	20.9	29.4	40.1	51.1	67.2	79.0
Circalittoral mixed sediment	3.07	0.0	<0.1	0.3	1.5	5.7	9.5	20.1	28.5	45.2	63.9
Infralittoral coarse sediment	1.11	<0.1	0.3	2.1	66.5	72.0	75.3	80.8	85.6	89.3	93.9
Infralittoral mud	0.29	0.0	0.0	<0.1	1.0	4.3	12.6	24.3	41.3	61.0	81.8
Infralittoral mixed sediment	0.03	0.0	0.0	<0.1	1.9	3.3	3.5	3.7	3.9	9.7	11.0
Offshore circalittoral rock and biogenic reef	0	1.0	1.4	3.8	3.8	9.3	31.8	31.8	31.8	100.0	100.0
Infralittoral rock and biogenic reef	0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	4.7	4.7	100.0
Circalittoral rock and biogenic reef	0	0.0	0.0	0.0	93.7	100.0	100.0	100.0	100.0	100.0	100.0

Fishing weight consequences, as a % relative to total weight, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral sand	69.03	0.4	1.5	5.4	10.4	16.0	22.1	29.6	37.4	46.1	58.6
Circalittoral sand	58.53	<0.1	0.3	1.6	3.8	6.9	11.4	15.5	20.2	27.2	39.1
Offshore circalittoral mud	29.48	3.2	7.5	15.6	26.0	34.9	44.4	55.0	65.1	76.5	88.8
Offshore circalittoral coarse sediment	14.15	<0.1	<0.1	0.6	3.5	7.9	14.9	25.0	40.2	56.2	75.3
Infralittoral sand	6.43	<0.1	0.3	4.5	9.8	23.2	38.8	47.5	54.5	63.8	80.3
Circalittoral coarse sediment	16.18	0.0	0.0	<0.1	<0.1	1.3	3.6	7.7	21.1	29.5	42.2
Unknown	2.2	0.0	0.0	0.8	2.3	5.5	12.3	21.8	36.6	52.8	71.5
Circalittoral mud	3.46	<0.1	0.4	2.8	6.1	9.0	11.8	14.2	83.5	88.4	94.9
Offshore circalittoral mixed sediment	1.9	0.2	1.3	8.9	16.9	24.5	32.7	44.2	54.7	75.8	85.1
Circalittoral mixed sediment	3.07	0.0	<0.1	0.4	2.6	7.2	11.8	18.9	26.4	41.9	59.1
Infralittoral coarse sediment	1.11	<0.1	0.2	2.4	53.4	60.3	63.2	70.8	78.5	81.5	86.0
Infralittoral mud	0.29	0.0	0.0	0.1	2.0	5.0	16.4	29.0	48.1	66.3	84.1
Infralittoral mixed sediment	0.03	0.0	0.0	<0.1	5.2	9.7	9.7	9.9	10.0	14.7	19.1
Offshore circalittoral rock and biogenic reef	0	1.6	2.1	5.5	5.5	14.1	43.3	43.3	43.3	100.0	100.0
Infralittoral rock and biogenic reef	0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	16.1	16.1	100.0
Circalittoral rock and biogenic reef	0	0.0	0.0	0.0	77.0	100.0	100.0	100.0	100.0	100.0	100.0

English Channel

Summary

The physical disturbance pressures from mobile bottom-contacting fishing gears is spatially heterogeneous in the English Channel. The subdivision is intensely fished (average intensity = 4.15 year-1) with 95% of the grid cells (I-2), and 68% of the surface area (I-3) being fished on average per year for the period 2013-2018 (Table 1). The subdivision is almost completely fished, with only 5% of the grid cells being unfished. Fishing is aggregated with 90% of the pressure occurring in 41% of grid cells (I-4).

The PD method shows an average decline in community biomass of 19% relative to carrying capacity across c-squares (I-6). The English Channel has the smallest portion of c-squares, 65% (I-7), with an impact score less than 20% compared to the other subdivisions of the Greater North Sea. However, the value might be influenced by the fact that almost the entire subdivision seafloor is impacted to some extent. The L1 method shows an average impact of 0.65 across c-squares (I-6). Only 18% (I-7) of the c-squares have impact scores less than 20% (I-7).

Maps of spatial distribution of intensity, seafloor sensitivity and economic value and weight of fisheries landings are shown in Figure 1. The seafloor sensitivity according to median longevity is among the lowest of the Greater North Sea as the predominant longevity class is 4-5 years. Highest value areas are located in the Bay of Seine and towards the eastern part of the channel. Highest landings come from the Bay of Seine.

Table 1

Table 1. Pressure and impact indicators for 2013-2018

Indicators	0 to 200 m	200 to 800 m	more than 800 m
Average intensity (I-1)	4.15	NA	NA
Proportion of area in fished cells (I-2)	0.95	NA	NA
Proportion of area fished per year (I-3)	0.68	NA	NA
Smallest prop. of area in fished cells with 90% of fishing effort (I-4)	0.41	NA	NA
Proportion of area in unfished cells (I-5)	0.05	NA	NA
Average PD impact (I-6)	0.19	NA	NA
Average L1 impact (I-6)	0.72	NA	NA
Proportion of area with PD impact < 0.2 (I-7)	0.65	NA	NA
Proportion of area with L1 impact < 0.2 (I-7)	0.18	NA	NA

Figure 1

Figure 1 Geographic distribution of surface abrasion, seabed sensitivity (community longevity) and total value and weight from mobile bottom-contacting gear. The maps of surface abrasion, value and weight show the average per year for 2013-2018

Pressure

The distribution of fishing intensity in the English Channel highlights the highest SAR in the Bay of Seine and in the eastern part of the channel and the lowest SAR around the Channel Islands and northeast of them (Figure 2).

The proportion of area subject to fishing pressure differs between broad-scale habitats but is above 80% for most of them. Grid cells within offshore circalittoral coarse sediments, offshore circalittoral mixed sediments and offshore circalittoral sand are 100% fished. (Table 2). Fishing intensity is highest in offshore circalittoral sand (average intensity = 6.43 year-1) and offshore circalittoral coarse sediments (average intensity = 5.46 year-1). The most extensive and most swept habitat is offshore circalittoral coarse sediments which outcome most of the landing and value.

Total fishing intensity increased overall for all broad-scale habitats between 2013 and 2018 (Figure 3). The increase in fishing intensity does not correspond to an increased proportion of area fished which is generally stable over time. However, the proportion of area corresponding to 90% of the effort decreased over time, meaning that fishing pressure became more aggregated (Figure 3, right panel).

Fishing pressure is aggregated, both at the regional level as well as at the level of the habitat (Figure 3, right panel). The smallest proportion of habitat with 90% of effort varies between 40-60%. Offshore circalittoral coarse sediment habitat is the most extensively fished over its surface however with the least aggregated fishing pressure. The core fishing grounds contribute to most of the landings and value in the English Channel. Both 60% of the landings and the value derive from 20% of its surface area (Figure 4).

Figure 2

Figure 2 Surface abrasion, Swept Area Ratio, by mobile bottom-contacting gears (year-1), averaged for the 2013-2018 six-year cycle

Table 2

Table 2 Overview of pressure indicators of all mobile bottom-contacting gears per broad-scale habitat averaged for 2013-2018. I refers to the indicators in Table 1.

MSFD broad habitat type	Extent of habitat (1000 km2)	Number of grid cells	Landings 1000 tonnes	Value 106 euro	Swept area 1000 km2	Average intensity (I-1)	Prop. of area in fished grid cells (I-2)	Prop. of area fished per year (I-3)	Smallest prop. of area with 90% of fishing effort (I-4)
Offshore circalittoral coarse sediment	27.22	1837	37.17	97.21	148.31	5.45	1.00	0.79	0.41
Circalittoral coarse sediment	10.05	1106	8.91	22.76	27.50	2.74	0.92	0.52	0.24
Circalittoral sand	4.54	695	4.64	12.86	17.26	3.80	0.96	0.76	0.34
Offshore circalittoral sand	2.62	475	5.32	15.19	16.73	6.39	1.00	0.97	0.37
Offshore circalittoral mixed sediment	1.76	179	1.03	2.38	5.17	2.93	1.00	0.80	0.39
Infralittoral sand	1.20	412	1.85	3.63	3.10	2.59	0.93	0.64	0.23
Circalittoral mud	0.68	157	0.46	1.41	2.15	3.17	0.95	0.63	0.20
Infralittoral coarse sediment	1.31	338	2.88	4.67	1.57	1.20	0.93	0.45	0.17
Offshore circalittoral mud	0.18	51	0.20	0.60	1.05	5.71	1.00	0.98	0.33
Infralittoral mud	0.23	114	0.32	0.82	0.66	2.91	0.88	0.68	0.18
Offshore circalittoral rock and biogenic reef	0.43	312	0.23	0.61	0.49	1.15	1.00	0.32	0.28
Circalittoral rock and biogenic reef	0.81	404	0.15	0.36	0.34	0.42	0.80	0.25	0.16
Unknown	0.42	275	0.06	0.14	0.25	0.60	0.82	0.29	0.09
Infralittoral rock and biogenic reef	0.35	283	0.27	0.51	0.25	0.71	0.75	0.20	0.09
Circalittoral mixed sediment	0.62	116	0.06	0.15	0.19	0.32	0.82	0.25	0.25
Infralittoral mixed sediment	0.01	21	0.00	0.00	0.00	0.10	0.20	0.10	0.05

Figure 3

Figure 3. Time series of (a) mean fishing intensity (surface abrasion), (b) proportion of the surface area of the seafloor fished, (c) aggregation of fishing (proportion of the surface area with 90% of the fishing effort) by habitat. Results represent vessels over 15m (2009-2011) and vessels over 12m (2012-2018).

Figure 4

Figure 4. Cumulative proportion of the swept area, landings and value. Grid cells were sorted from highest to lowest fishing intensity and include non-fished cells. The results are for all mobile bottom-contacting gears based on averaged fishing data per c-square from 2013-2018.

Core fishing grounds

Core fishing grounds are defined as the c-squares with the 90% highest value of landings in the VMS data. Figure 5 shows the number of years c-squares are within the 90% highest value by métier. If fishing in a métier occurs in the same c-square every year with high value of landings, the rightmost bar in Figure 5 and 6 will be high, meaning that the c-square is within the 90% highest value of landings every year during the period 2013-2018. If a c-square is only within the 90% highest value in one year, it will end up in the bar at the left. Figure 6 shows the percentage area overlap between the 90% highest value per year and the reference fishing ground.

In the English Channel, the core fishing grounds of dredges for mollusks (DRB_MOL) and otter trawl for demersal fish (OT_DMF) are the most stable over time. Oppositely, core grounds for otter trawl targeting crustaceans (OT_CRU) and the seine (SSC_DMF, SDN_DMF) have the highest variation in space.

Figure 7 illustrates the relationship between area fished in percent and the cumulated value of landings, sorted from the c-squares with highest value fisheries. The curves are generally starting steeply, illustrating the concentration of the fisheries at fishing grounds and the curves are ending horizontally, illustrating the peripheral fisheries going on outside the main fishing grounds.

Figure 5

Figure 5. Number of years c-squares are within the 90% core fishing grounds by metier during the period 2013-2018

Figure 6

Figure 6. Percentage area overlap between the 90% highest value per year and the reference core fishing ground

Figure 7

Figure 7. Percent area fished vs. landings value (euro) by métier, coloured by year

Fishing by métier

Intensity, weight and value of landings are estimated for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers (Table 3).

The métier with the highest landings and value per area fished is the beam trawl fishery for whelks, snails and scallop (TBB_MOL) and the dredge for mussels and scallop (DRB_MOL) despite smaller areas, especially for the beam trawl métier, were swept compared to the other métiers. The seines (SDN_DMF and SSC_DMF) have the lowest landings and value per area fished.

Table 3

Table 3. Overview of area fished (sum of swept area), landings and value for the different metiers. Area fished in 1000 km², weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Area swept (1000 km2)	7.36	1.76	71.71	25.67	4.86	20.84	78.05	0.01	13.01	0.01
Landings (1000 tonnes)	26.77	0.09	12.38	11.44	1.70	1.65	5.59	<0.005	3.67	0.20
Value (10^6 euro)	73.74	0.70	28.15	26.88	3.02	4.20	12.43	0.03	13.73	0.16
Landings (1000 tonnes)/Area swept (1000 km2)	3.64	0.05	0.17	0.45	0.35	0.08	0.07	0.32	0.28	36.68
Value (10^6 euro)/Area swept (1000 km2)	10.02	0.40	0.39	1.05	0.62	0.20	0.16	2.24	1.05	28.90

Impact

The impact of mobile bottom-contacting fishing calculated from both the PD and L1 methods mimics the distribution of fishing intensity. The areas of highest fishing impact using the PD method are in the Bay of Seine and in the eastern part of the channel (Figure 8, left). According to the L1 method, areas with impact above 0.8 are vastly distributed along the English Channel except in the surrounding of the Channel Islands and northeast of them (Figure 8, right).

The impact scores are largely constant over time (Figure 9, left panels). Impact varies between the four most extensive habitat types, with offshore circalittoral sand being the most impacted according to both indicators. The offshore circalittoral sand habitat has the lowest proportion of area with impact below 0.2 (less than 10% using the L1 method), while circalittoral coarse sediment habitat has the most.

Table 4 shows impact per métier relative to weight and value of landings. In this analysis, the different métiers are assessed for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers. As such this estimates the maximum impact compared to the untrawled situation and the impact estimated assuming all other métiers to have impacted the habitat will be less than this. The métiers with the highest impact (PD and L1) relative to the value and landings are the ones targeting demersal fish (OT_DMF, SDN_DMF). The métiers targeting mollusks (DRB_MOL and TBB_MOL) have the lowest impact relative to value and landing, although this is influenced by the smaller swept area (Table 3).

Métiers differ in their habitat association and impact on each habitat type (Figure 10). Fishing impact in the English Channel is comparable among métiers. The most impacted broad-scale habitat type by several métiers is the offshore circalittoral sand, followed by offshore circalittoral coarse sediments. The highest impacts are caused by métiers targeting demersal fish, including otter trawl (OT_DMF), seines (SDN_DMF) and beam trawl (TBB_DMF).

Figure 8

Figure 8. Impact of mobile bottom-contacting gears averaged for the 2013-2018 six-year cycle for the PD and L1 method.

Figure 9

Figure 9. The mean impact of mobile bottom-contacting gears in all combined MSFD habitats and the four most extensive habitat types between 2009 and 2018 (left). The proportion of the fished area with an impact of less than 0.2 (right)

Table 4

Table 4. Overview of impact per metier relative to weight and value of landings estimated for the grid cells fished (SAR >0) with these métiers only. Weight of landings in 1000 tonnes, value of landings in 10⁶ euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Landings (1000 tonnes)/PD impact	0.271	0.007	0.093	0.088	0.142	0.091	0.065	0.040	0.029	1.465
Value (10^6 euro)/PD impact	0.746	0.054	0.212	0.207	0.252	0.232	0.145	0.284	0.108	1.154
Landings (1000 tonnes)/L1 impact	0.049	0.001	0.007	0.012	0.006	0.003	0.007	0.007	0.005	0.669
Value (10^6 euro)/L1 impact	0.135	0.005	0.017	0.027	0.010	0.009	0.015	0.049	0.018	0.527

Figure 10

Figure 10. PD impact (upper panel) and L1 impact (lower panel) of selected gear groupings on the most extensive MSFD habitat types. Impact is estimated in isolation of the other gear groupings. Note the different scales on the Y-axis.

Management scenarios

The figures and tables below show one implementation of multi-purpose habitat management through reductions in effort and spatial closures for the four most extensive MSFD habitat types. They show the changes in average impact (PD, L1), unfished area and fisheries values of landings based on a static assessment of effort removal.

The analysis is based on the progressive removal of 5 to 99% of all MBCG fishing effort, starting from the c-squares with the lowest effort (corrected for the areal extent of the MSFD habitat within each c-square). Blue dots show the current situation and are used as reference. The % of unfished area in the reference is only based on grid cells that are unfished. Average PD and L1 impacts are a weighted average and consider the areal extent of each MSFD habitat type within a grid cell.

Note that the fraction of grid cells above/below a certain impact threshold initially remains the same (not shown) as the removal of effort starts from the c-squares with the lowest effort that typically have low impact.

In the English Channel, 52% of the total area is represented by offshore circalittoral coarse sediments. Remarkably, the analysis highlights that 5% effort removal within this habitat type already consists in the percentage of unfished areas rising above 38%. However, the area lost corresponds only to less than 10% loss in value and landings. The impact indicators already show an improvement, especially according to the L1 method.

MSFD habitat - 1

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.24	0.83	0.49	100.00	100.00
5	0.21	0.61	38.54	94.78	94.76
10	0.20	0.51	49.12	88.59	88.63
15	0.18	0.43	56.93	81.61	81.79
20	0.16	0.37	63.02	73.86	74.36
30	0.14	0.27	72.58	60.26	61.07
40	0.11	0.20	79.95	47.66	48.69
60	0.06	0.10	90.15	27.38	28.22
80	0.02	0.03	97.24	8.94	8.91
99	0.00	0.00	100.00	0.40	0.37

MSFD habitat - 2

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.12	0.57	7.59	100.00	100.00
5	0.11	0.42	56.45	91.44	87.93
10	0.10	0.34	65.85	85.81	82.51
15	0.09	0.27	72.84	79.31	76.23
20	0.08	0.22	77.74	75.13	71.73
30	0.07	0.15	85.10	64.35	60.92
40	0.06	0.11	89.19	52.49	49.59
60	0.03	0.06	94.27	30.47	28.82
80	0.02	0.02	97.75	15.87	15.32
99	0.00	0.00	100.00	4.18	4.29

MSFD habitat - 3

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.17	0.79	4.03	100.00	100.00
5	0.15	0.64	33.85	92.99	91.76
10	0.14	0.52	47.42	87.76	85.94
15	0.13	0.44	55.88	81.78	79.18
20	0.12	0.37	62.69	75.04	73.43
30	0.10	0.28	72.23	64.17	62.78
40	0.08	0.21	79.62	56.17	54.41
60	0.05	0.11	89.52	33.78	31.32
80	0.03	0.04	95.94	16.59	15.46
99	0.00	0.00	100.00	1.15	1.33

MSFD habitat - 4

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	0.34	0.97	0.01	100.00	100.00
5	0.32	0.84	15.09	93.30	92.88
10	0.30	0.74	25.51	86.58	86.62
15	0.28	0.67	33.30	81.69	82.16
20	0.26	0.59	41.12	76.22	77.24
30	0.22	0.48	52.63	62.05	63.65
40	0.18	0.36	63.67	51.53	53.77
60	0.11	0.19	81.44	28.33	30.16
80	0.05	0.08	92.21	12.29	13.68
99	0.01	0.01	100.00	1.56	1.86

Overview all MSFD habitats

Fishing effort consequences, as a % relative to total swept area, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral coarse sediment	27.22	<0.1	0.2	0.6	2.2	5.7	10.6	17.4	27.1	40.2	59.7
Circalittoral coarse sediment	10.05	0.0	<0.1	<0.1	0.4	1.4	3.0	6.6	12.5	23.1	43.4
Circalittoral sand	4.54	<0.1	0.2	1.4	4.0	7.3	11.4	18.4	27.7	40.7	62.1
Offshore circalittoral sand	2.62	0.9	2.7	7.6	13.2	19.4	28.2	37.0	47.8	59.2	76.9
Offshore circalittoral mixed sediment	1.76	<0.1	0.3	1.9	5.3	12.5	19.1	26.7	40.3	51.8	70.2
Infralittoral sand	1.2	0.0	<0.1	0.4	1.8	5.0	11.7	19.8	37.7	52.1	76.0
Circalittoral mud	0.68	<0.1	0.1	1.2	2.5	4.7	7.6	13.4	21.1	33.4	61.7
Infralittoral coarse sediment	1.31	0.0	<0.1	0.2	1.0	3.0	7.3	15.6	22.4	32.8	59.4
Offshore circalittoral mud	0.18	1.4	5.4	14.5	17.2	20.3	30.7	34.6	38.7	42.8	67.3
Infralittoral mud	0.23	0.0	0.0	0.3	1.9	6.4	12.5	18.4	42.1	58.4	85.8
Offshore circalittoral rock and biogenic reef	0.43	0.6	1.2	2.8	4.4	6.0	7.4	9.9	12.7	18.4	27.1
Circalittoral rock and biogenic reef	0.81	0.0	0.0	0.0	0.6	2.3	6.6	11.9	22.6	39.0	55.3
Unknown	0.42	0.0	0.0	<0.1	0.9	2.8	4.0	7.4	14.3	22.8	40.1
Infralittoral rock and biogenic reef	0.35	0.0	0.0	0.0	<0.1	0.2	0.6	1.1	2.7	5.4	25.7
Circalittoral mixed sediment	0.62	0.0	0.0	<0.1	0.7	1.4	3.1	11.1	22.7	41.2	64.8
Infralittoral mixed sediment	0.01	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	100.0

Fishing value consequences, as a % relative to total value, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral coarse sediment	27.22	<0.1	0.2	0.4	1.9	6.2	12.4	22.8	36.2	52.5	72.5
Circalittoral coarse sediment	10.05	0.0	<0.1	0.2	1.1	3.1	5.7	11.2	18.1	28.3	52.7
Circalittoral sand	4.54	<0.1	0.7	2.5	6.0	10.0	14.2	22.7	34.2	44.9	68.0
Offshore circalittoral sand	2.62	1.4	3.5	10.4	16.7	23.5	36.7	46.6	56.7	69.7	85.3
Offshore circalittoral mixed sediment	1.76	<0.1	0.2	1.9	6.4	15.4	21.6	29.0	45.3	56.1	74.8
Infralittoral sand	1.2	0.0	<0.1	1.4	4.8	11.2	18.4	26.8	45.0	58.9	81.4
Circalittoral mud	0.68	<0.1	0.3	1.8	3.8	7.4	12.1	17.7	23.8	36.0	62.0
Infralittoral coarse sediment	1.31	0.0	<0.1	0.2	1.9	5.5	12.7	23.9	39.1	57.1	76.0
Offshore circalittoral mud	0.18	3.2	7.6	21.8	25.9	28.9	38.4	41.7	44.0	46.6	70.4
Infralittoral mud	0.23	0.0	0.0	1.2	6.2	21.0	33.3	37.2	63.3	73.7	92.8
Offshore circalittoral rock and biogenic reef	0.43	0.7	1.1	1.7	2.2	3.0	5.2	6.1	8.0	10.8	16.7
Circalittoral rock and biogenic reef	0.81	0.0	0.0	0.0	0.7	3.8	19.8	23.5	33.1	47.3	62.6
Unknown	0.42	0.0	0.0	0.1	1.2	7.5	9.3	12.2	20.2	34.4	49.3
Infralittoral rock and biogenic reef	0.35	0.0	0.0	0.0	<0.1	0.7	1.5	3.6	8.4	15.4	49.4
Circalittoral mixed sediment	0.62	0.0	0.0	<0.1	0.8	1.6	3.3	9.7	20.1	50.0	61.0
Infralittoral mixed sediment	0.01	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	100.0

Fishing weight consequences, as a % relative to total weight, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Offshore circalittoral coarse sediment	27.22	<0.1	0.2	0.5	1.9	6.3	12.3	22.2	35.4	51.5	71.7
Circalittoral coarse sediment	10.05	0.0	<0.1	0.2	2.1	6.7	9.4	14.5	21.2	32.0	55.0
Circalittoral sand	4.54	0.2	1.4	3.6	7.0	11.9	16.3	25.0	35.7	46.5	70.5
Offshore circalittoral sand	2.62	1.7	4.0	10.7	16.3	22.4	35.0	44.3	54.9	67.8	84.5
Offshore circalittoral mixed sediment	1.76	<0.1	0.2	1.8	5.9	13.8	19.8	27.2	42.0	52.8	72.8
Infralittoral sand	1.2	0.0	<0.1	1.5	6.0	19.4	25.7	32.5	44.7	56.7	84.1
Circalittoral mud	0.68	<0.1	0.4	2.3	4.5	8.3	13.1	20.7	27.0	37.9	62.7
Infralittoral coarse sediment	1.31	0.0	<0.1	0.2	1.6	4.4	15.7	34.6	48.2	63.1	79.3
Offshore circalittoral mud	0.18	3.1	7.9	20.6	23.3	25.9	35.5	38.5	40.6	43.0	69.5
Infralittoral mud	0.23	0.0	0.0	3.1	9.7	35.4	46.6	49.4	76.1	82.6	94.2
Offshore circalittoral rock and biogenic reef	0.43	1.3	1.6	2.3	2.8	3.6	7.5	8.4	10.6	13.5	19.1
Circalittoral rock and biogenic reef	0.81	0.0	0.0	0.0	0.7	3.6	29.9	32.9	40.9	56.8	68.6
Unknown	0.42	0.0	0.0	0.1	1.4	7.2	8.8	11.5	19.2	31.8	46.7
Infralittoral rock and biogenic reef	0.35	0.0	0.0	0.0	<0.1	0.8	1.9	4.0	9.2	17.6	58.4
Circalittoral mixed sediment	0.62	0.0	0.0	<0.1	1.1	2.1	3.2	8.9	18.6	48.0	60.2
Infralittoral mixed sediment	0.01	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	100.0

Norwegian Trench

Summary

The physical disturbance pressures from mobile bottom-contacting fishing gears in the Norwegian Trench is spatially concentrated due to the bathymetrical conditions of the area according to which 50% of the grid cells are not fished because of large depths (I-5). Consequently, 50% of the grid cells (I-2), and 35% of the surface area (I-3), in the depth zone 0-200m, are fished on average per year for the period 2013-2018 (Table 1). Fishing is strongly aggregated along the trench with 90% of the pressure occurring in 21% of grid cells (I-4). The average fishing intensity is 2.51 but the large portion of unfished area should be considered. Along the trench, SAR exceeds 10.

Impact indicators could not be calculated for this subdivision because of data unavailability.

Maps of spatial distribution of intensity, seafloor sensitivity and economic value and weight of fisheries landings are shown in Figure 1. Landings and values are also spatially heterogeneous. Landings are highest along the northern part of the trench, while value is the highest in the southern part in between Norway and Denmark.

Table 1

Table 1. Pressure and impact indicators for 2013-2018

Indicators	0 to 200 m	200 to 800 m	more than 800 m
Average intensity (I-1)	2.51	1.65	0
Proportion of area in fished cells (I-2)	0.47	0.53	0
Proportion of area fished per year (I-3)	0.37	0.34	0
Smallest prop. of area in fished cells with 90% of fishing effort (I-4)	0.22	0.20	NA
Proportion of area in unfished cells (I-5)	0.53	0.47	1
Average PD impact (I-6)	NA	NA	NA
Average L1 impact (I-6)	NA	NA	NA
Proportion of area with PD impact < 0.2 (I-7)	NA	NA	NA
Proportion of area with L1 impact < 0.2 (I-7)	NA	NA	NA

Figure 1

Figure 1 Geographic distribution of surface abrasion, seabed sensitivity (not shown) and total value and weight from mobile bottom-contacting gear. The maps of surface abrasion, value and weight show the average per year for 2013-2018

Pressure

The distribution of fishing intensity in the Norwegian Trench has a strong spatial variation due to geological conditions of the area. (Figure 2). Areas of higher intensity occur outside of the trench with an intensely fished area between Norway and Denmark. Areas with lower intensity occur along the slope of the trench.

Fishing intensity is highest in offshore circalittoral sand (average intensity = 14.2 year-1) followed by offshore circalittoral mud (average intensity = 5.29 year-1) and circalittoral sand (average intensity = 4.45 year-1). The proportion of area subject to fishing pressure differs between broad-scale habitats going from 20 to 99%. The highest proportion of area covered occurs in the three most intensely fished habitats (offshore circalittoral sand with 98% of grid cells fished, offshore circalittoral mud with 93% of grid cells fished, and circalittoral sand with 99% of grid cells fished) (Table 2). The largest portion of swept area covers the upper bathyal sediment habitat from which the largest portion of landing and value come from. However, up to 57% of the grid cells is fished and intensity is 1.75 on average.

Total fishing intensity decreased over time in offshore circalittoral mud habitat (Figure 3). A peak of intensity in 2016 is displayed for the other habitats, although possibly coming from erroneous data. The proportion of area fished remained constant for offshore circalittoral mud, while it seems to increase over time for the other habitats. The same pattern is visible for the core fishing grounds, where the proportion of area covering 90% of the effort seems to expand over time (effort less aggregated over time). Fishing pressure is still very aggregated, both at the regional level as well as at the level of the habitat (Figure 3, right panel). The smallest proportion of habitat with 90% of effort varies between 8-40%. These grounds strongly contribute to the landings and value as it is displayed by the steep cumulative curve in Figure 4. Over 80% of the fishing effort (swept area) landings and value occur in less than 20% of the surface area of the Norwegian Trench.

Figure 2

Figure 2 Surface abrasion, Swept Area Ratio, by mobile bottom-contacting gears (year-1), averaged for the 2013-2018 six-year cycle

Table 2

Table 2 Overview of pressure indicators of all mobile bottom-contacting gears per broad-scale habitat averaged for 2013-2018. I refers to the indicators in Table 1.

MSFD broad habitat type	Extent of habitat (1000 km2)	Number of grid cells	Landings 1000 tonnes	Value 106 euro	Swept area 1000 km2	Average intensity (I-1)	Prop. of area in fished grid cells (I-2)	Prop. of area fished per year (I-3)	Smallest prop. of area with 90% of fishing effort (I-4)
Upper bathyal sediment	69.96	4209	41.53	25.95	108.84	1.56	0.52	0.33	0.22
Offshore circalittoral mud	8.32	1037	11.04	26.72	43.83	5.27	0.93	0.83	0.38
Offshore circalittoral sand	3.02	413	13.18	17.73	42.89	14.20	0.98	0.96	0.40
Circalittoral sand	3.65	405	9.66	8.66	16.22	4.45	0.99	0.88	0.42
Offshore circalittoral rock and biogenic reef	3.95	1846	0.25	0.73	3.88	0.98	0.42	0.29	0.08
Offshore circalittoral mixed sediment	0.89	272	0.58	1.71	3.09	3.47	0.96	0.66	0.26
Unknown	5.95	1979	0.10	0.00	2.66	0.45	0.29	0.14	0.04
Circalittoral mixed sediment	0.53	271	1.74	1.12	1.83	3.48	0.93	0.70	0.18
Upper bathyal rock and biogenic reef	2.53	1105	0.12	0.01	1.63	0.64	0.21	0.17	0.06
Infralittoral sand	0.27	153	0.21	0.35	0.94	3.48	0.91	0.70	0.20
Upper bathyal sediment or Upper bathyal rock and biogenic reef	2.81	1053	0.06	0.00	0.82	0.29	0.16	0.11	0.03
Circalittoral rock and biogenic reef	1.05	1669	0.03	0.17	0.48	0.45	0.31	0.14	0.06
Infralittoral rock and biogenic reef	0.67	1660	0.01	0.08	0.26	0.40	0.27	0.13	0.05
Circalittoral mud	0.34	253	0.01	0.04	0.11	0.32	0.36	0.17	0.11
Infralittoral mud	0.16	215	0.00	0.01	0.07	0.42	0.32	0.16	0.06
Offshore circalittoral coarse sediment	0.04	128	0.01	0.05	0.07	1.54	0.95	0.48	0.25
Circalittoral coarse sediment	0.04	125	0.01	0.05	0.05	1.12	0.85	0.43	0.14
Infralittoral coarse sediment	0.01	104	0.00	0.02	0.02	1.54	0.66	0.37	0.07
Infralittoral mixed sediment	0.03	146	0.01	0.01	0.01	0.39	0.36	0.16	0.06
Lower bathyal rock and biogenic reef	0.00	3	0.00	0.00	0.00	0.00	0.00	0.00	NA
Lower bathyal sediment or Lower bathyal rock and biogenic reef	0.00	5	0.00	0.00	0.00	0.00	0.00	0.00	NA

Figure 3

Figure 3. Time series of (a) mean fishing intensity (surface abrasion), (b) proportion of the surface area of the seafloor fished, (c) aggregation of fishing (proportion of the surface area with 90% of the fishing effort) by habitat. Results represent vessels over 15m (2009-2011) and vessels over 12m (2012-2018).

Figure 4

Figure 4. Cumulative proportion of the swept area, landings and value. Grid cells were sorted from highest to lowest fishing intensity and include non-fished cells. The results are for all mobile bottom-contacting gears based on averaged fishing data per c-square from 2013-2018.

Core fishing grounds

Core fishing grounds are defined as the c-squares with the 90% highest value of landings in the VMS data. Figure 5 shows the number of years c-squares are within the 90% highest value by métier. If fishing in a métier occurs in the same c-square every year with high value of landings, the rightmost bar in Figure 5 and 6 will be high, meaning that the c-square is within the 90% highest value of landings every year during the period 2013-2018. If a c-square is only within the 90% highest value in one year, it will end up in the bar at the left. Figure 6 shows the percentage area overlap between the 90% highest value per year and the reference fishing ground. Both figures highlight that the otter trawl fishery for demersal fish (OT_DMF) and for crustaceans (OT_CRU) together with beam trawl fishery for demersal fish (TBB_DMF) are the most stable and overlapping over time. On the other hand, the core grounds of seines (SSC_DMF, SDN_DMF) and otter trawl for demersal fish (OT_SPF) have the highest variation in space.

Figure 7 illustrates the relationship between area fished in percent and the cumulated value of landings, sorted from the c-squares with highest value fisheries. The curves are generally starting steeply, illustrating the concentration of the fisheries at fishing grounds and the curves are ending horizontally, illustrating the peripheral fisheries going on outside the main fishing grounds.

Figure 5

Figure 5. Number of years c-squares are within the 90% core fishing grounds by metier during the period 2013-2018

Figure 6

Figure 6. Percentage area overlap between the 90% highest value per year and the reference core fishing ground

Figure 7

Figure 7. Percent area fished vs. landings value (euro) by métier, coloured by year

Fishing by métier

Intensity, weight and value of landings are estimated for the grid cells that were fished by one MBCG métier, ignoring cells fished by other métiers (Table 3).

The métier with the highest landings and value per area fished is the beam trawl fishery for demersal fish (TBB_DMF) but note that the métier covers the smallest swept area among the active ones. The seines (SDN_DMF and SSC_DMF) have the lowest landings, but comparable ratios with the otter trawl métiers (OT_DMF and OT_CRU).

Table 3

Table 3. Overview of area fished (sum of swept area), landings and value for the different metiers. Area fished in 1000 km2, weight of landings in 1000 tonnes, value of landings in 10^6 euro.

	DRB_MOL	OT_CRU	OT_DMF	OT_MI	OT_SPF	SDN_DMF	SSC_DMF	TBB_CRU	TBB_DMF	TBB_MOL
Area swept (1000 km2)	<0.005	97.61	88.65	<0.005	5.75	24.88	10.88	<0.005	1.30	0
Landings (1000 tonnes)	0	10.84	35.81	0.01	24.80	4.46	1.13	<0.005	1.47	0
Value (10^6 euro)	0	41.34	28.97	0	0.13	8.18	2.24	<0.005	2.84	0
Landings (1000 tonnes)/Area swept (1000 km2)	0	0.11	0.40	1.51	4.31	0.18	0.10	0.12	1.13	NaN
Value (10^6 euro)/Area swept (1000 km2)	0	0.42	0.33	0	0.02	0.33	0.21	0.59	2.19	NaN

Impact

No information available

Management scenarios

The figures and tables below show one implementation of multi-purpose habitat management through reductions in effort and spatial closures for the four most extensive MSFD habitat types. As the impact indicators could not be calculated for the Norwegian Trench, the analysis only shows the changes in proportion of unfished area, fisheries values of landings based on a static assessment of effort removal.

The analysis is based on the progressive removal of 5 to 99% of all MBCG fishing effort, starting from the c-squares with the lowest effort (corrected for the areal extent of the MSFD habitat within each c-square). Blue dots show the current situation and are used as reference. The % of unfished area in the reference is only based on grid cells that are unfished.

Among the three most extensive broad-scale habitat types (without considering the data classified under an unknown habitat type), only the offshore circalittoral mud habitat (among the most intensely fished) shows a gradual increase in unfished area, while the others rapidly lose more than 50% of the original area once reducing the effort above 20%.

MSFD habitat - 1

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	NA	NA	47.56	100.00	100.00
5	NA	NA	73.82	96.54	94.22
10	NA	NA	79.38	92.26	87.97
15	NA	NA	82.55	88.69	81.82
20	NA	NA	84.92	84.74	72.94
30	NA	NA	88.48	74.54	61.60
40	NA	NA	91.23	58.29	51.03
60	NA	NA	95.47	25.53	32.05
80	NA	NA	98.34	8.52	14.05
99	NA	NA	99.98	0.58	0.68

MSFD habitat - 2

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	NA	NA	7.03	100.00	100.00
5	NA	NA	30.20	96.87	93.75
10	NA	NA	39.02	93.26	88.26
15	NA	NA	45.81	89.20	83.11
20	NA	NA	50.82	84.05	78.57
30	NA	NA	60.69	73.65	68.99
40	NA	NA	68.79	63.16	60.70
60	NA	NA	81.54	44.78	40.40
80	NA	NA	92.04	21.33	20.49
99	NA	NA	99.88	0.58	3.26

MSFD habitat - 3

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	NA	NA	2.32	100.00	100.00
5	NA	NA	14.73	94.56	92.32
10	NA	NA	23.06	88.75	85.43
15	NA	NA	30.43	82.64	76.15
20	NA	NA	37.25	76.86	71.93
30	NA	NA	49.41	66.01	61.84
40	NA	NA	59.70	54.61	53.17
60	NA	NA	77.13	34.87	28.80
80	NA	NA	90.44	16.16	12.03
99	NA	NA	100.00	0.99	0.65

MSFD habitat - 4

Multi-purpose habitat management trade-off for the most extensive MSFD habitat type.

Table presenting a similar overview as above, while including weight of landings

Effort reduction (%)	Average PD impact	Average L1 impact	Area unfished (%)	Value (%)	Weight (%)
0	NA	NA	0.90	100.00	100.00
5	NA	NA	28.81	93.63	95.82
10	NA	NA	37.35	87.64	91.09
15	NA	NA	44.35	81.82	83.58
20	NA	NA	49.43	76.48	78.84
30	NA	NA	60.83	64.34	65.42
40	NA	NA	70.22	54.21	49.08
60	NA	NA	84.54	35.84	29.78
80	NA	NA	94.33	16.70	13.37
99	NA	NA	100.00	2.12	1.31

Overview all MSFD habitats

Fishing effort consequences, as a % relative to total swept area, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Upper bathyal sediment	69.96	0.0	0.0	0.0	0.0	0.0	<0.1	0.5	3.1	10.9	35.4
Offshore circalittoral mud	8.32	0.0	<0.1	1.2	4.9	11.1	19.4	29.4	41.9	57.4	76.5
Offshore circalittoral sand	3.02	0.3	2.7	8.4	15.2	22.4	31.3	40.8	51.3	64.1	80.1
Circalittoral sand	3.65	<0.1	0.5	2.4	5.9	12.0	20.8	29.9	40.4	53.7	71.7
Offshore circalittoral rock and biogenic reef	3.95	0.0	0.0	0.0	0.0	0.0	0.0	<0.1	4.2	16.1	46.5
Offshore circalittoral mixed sediment	0.89	<0.1	<0.1	0.3	1.8	4.8	11.0	18.5	29.0	46.1	67.4
Unknown	5.95	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.1	11.3
Circalittoral mixed sediment	0.53	0.0	<0.1	0.8	3.2	6.6	13.0	24.1	37.3	51.1	70.1
Upper bathyal rock and biogenic reef	2.53	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.2	23.5
Infralittoral sand	0.27	0.0	<0.1	0.2	1.1	4.7	10.4	22.0	37.5	56.5	77.5
Upper bathyal sediment or Upper bathyal rock and biogenic reef	2.81	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	6.4
Circalittoral rock and biogenic reef	1.05	0.0	0.0	0.0	0.0	0.0	0.0	0.0	<0.1	1.9	16.0
Infralittoral rock and biogenic reef	0.67	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.6	9.5
Circalittoral mud	0.34	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.8	10.6	40.3
Infralittoral mud	0.16	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.1	3.6	22.3
Offshore circalittoral coarse sediment	0.04	0.0	<0.1	0.4	1.2	2.9	5.7	9.0	23.2	40.2	79.1
Circalittoral coarse sediment	0.04	0.0	0.0	0.2	0.2	0.6	2.4	9.7	32.9	41.1	50.0
Infralittoral coarse sediment	0.01	0.0	0.0	0.0	0.0	<0.1	0.1	1.0	7.3	35.0	49.7
Infralittoral mixed sediment	0.03	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.7	4.4	36.2
Lower bathyal rock and biogenic reef	0	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN
Lower bathyal sediment or Lower bathyal rock and biogenic reef	0	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN

Fishing value consequences, as a % relative to total value, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Upper bathyal sediment	69.96	0.0	0.0	0.0	0.0	0.0	<0.1	0.4	2.1	8.7	33.5
Offshore circalittoral mud	8.32	0.0	<0.1	0.6	3.0	7.6	15.5	25.9	39.1	52.7	74.2
Offshore circalittoral sand	3.02	0.4	2.7	9.5	17.8	26.5	35.7	46.5	58.1	70.4	84.6
Circalittoral sand	3.65	0.1	0.6	3.3	7.2	14.3	25.0	35.7	46.3	58.7	74.4
Offshore circalittoral rock and biogenic reef	3.95	0.0	0.0	0.0	0.0	0.0	0.0	0.1	3.6	19.0	59.1
Offshore circalittoral mixed sediment	0.89	<0.1	<0.1	0.3	1.8	5.5	12.7	19.4	30.5	46.0	67.1
Unknown	5.95	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	39.9	42.3
Circalittoral mixed sediment	0.53	0.0	0.1	1.0	3.6	9.0	16.8	28.9	40.4	54.6	74.8
Upper bathyal rock and biogenic reef	2.53	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	9.2	81.8
Infralittoral sand	0.27	0.0	<0.1	0.2	1.8	5.8	11.1	24.8	41.1	58.7	80.7
Upper bathyal sediment or Upper bathyal rock and biogenic reef	2.81	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	100.0
Circalittoral rock and biogenic reef	1.05	0.0	0.0	0.0	0.0	0.0	0.0	0.0	<0.1	1.3	9.1
Infralittoral rock and biogenic reef	0.67	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.5	7.1
Circalittoral mud	0.34	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.0	13.0	42.9
Infralittoral mud	0.16	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.5	14.4	76.5
Offshore circalittoral coarse sediment	0.04	0.0	<0.1	0.4	1.0	2.3	4.8	7.3	19.7	36.5	81.0
Circalittoral coarse sediment	0.04	0.0	0.0	0.1	0.2	0.5	1.4	7.1	29.7	33.7	46.9
Infralittoral coarse sediment	0.01	0.0	0.0	0.0	0.0	<0.1	<0.1	0.5	4.4	32.3	47.9
Infralittoral mixed sediment	0.03	0.0	0.0	0.0	0.0	0.0	0.0	0.0	1.2	4.9	38.1
Lower bathyal rock and biogenic reef	0	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN
Lower bathyal sediment or Lower bathyal rock and biogenic reef	0	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN

Fishing weight consequences, as a % relative to total weight, of protecting a certain fraction of each broad habitat type sorted from low to high fished c-squares

MSFD broad habitat type	Extent of habitat 1000 km2	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Upper bathyal sediment	69.96	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	1.1	3.3	13.2	45.1
Offshore circalittoral mud	8.32	<0.1	0.3	2.0	6.2	13.4	21.0	30.7	40.7	57.5	76.6
Offshore circalittoral sand	3.02	0.4	4.0	12.2	24.0	30.5	39.0	47.5	58.0	74.2	88.4
Circalittoral sand	3.65	<0.1	0.4	2.2	4.8	11.2	23.2	34.6	51.1	63.0	78.8
Offshore circalittoral rock and biogenic reef	3.95	<0.1	0.2	0.2	0.2	0.2	0.3	0.6	8.9	23.9	61.5
Offshore circalittoral mixed sediment	0.89	<0.1	<0.1	0.2	1.0	2.8	7.3	10.5	17.3	36.0	64.5
Unknown	5.95	<0.1	<0.1	<0.1	1.0	1.0	1.0	1.0	1.0	4.6	28.2
Circalittoral mixed sediment	0.53	0.0	<0.1	0.4	2.6	6.3	12.6	23.5	31.2	45.3	75.9
Upper bathyal rock and biogenic reef	2.53	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	0.5	26.7
Infralittoral sand	0.27	0.0	<0.1	0.3	1.5	5.1	9.9	27.8	44.5	63.2	84.4
Upper bathyal sediment or Upper bathyal rock and biogenic reef	2.81	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	8.5
Circalittoral rock and biogenic reef	1.05	<0.1	<0.1	0.7	0.7	0.7	0.7	0.7	0.7	4.6	18.7
Infralittoral rock and biogenic reef	0.67	<0.1	<0.1	0.4	0.4	0.4	0.4	0.4	0.4	2.4	12.1
Circalittoral mud	0.34	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	1.1	21.9	57.7
Infralittoral mud	0.16	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	0.2	8.1	56.9
Offshore circalittoral coarse sediment	0.04	0.0	<0.1	0.4	1.3	2.5	6.4	8.4	32.3	46.1	85.0
Circalittoral coarse sediment	0.04	0.0	0.0	0.1	0.1	0.4	1.9	7.2	44.0	46.5	67.3
Infralittoral coarse sediment	0.01	0.0	0.0	0.0	0.0	<0.1	0.1	1.5	5.5	33.6	47.9
Infralittoral mixed sediment	0.03	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.1	0.4	17.3
Lower bathyal rock and biogenic reef	0	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN
Lower bathyal sediment or Lower bathyal rock and biogenic reef	0	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN

Read me

WKTRADE3 developed an assessment of fishing footprint of mobile bottom-contacting fishing gears (MBCG) and benthic impact that is appropriate for a six-year management cycle of MSFD assessments. The assessment maps and pressure and impact indicator values produced are based on an average fishing intensity of 2013-2018. This assessment period is linked to the latest available fishing data, rather than to the MSFD Art 8 assessment periods. The assessment product further shows year-to-year variation in pressure and impact from 2009.

The assessment presents five pressure indicators and two benthic impact indicators by (sub-)regional, subdivision sea, or broadscale habitat type within that sea (Table 1), following ICES 2017 advice. The assessment further describes spatial and temporal variation of core MBCG fishing footprints. Lastly, the assessment describes a trade-off analysis between fisheries and the seafloor based on a management scenario where fishing effort is reduced through spatial closures in each broadscale habitat type.

Table 1. Pressure and impact indicators that are applied by (sub-)regional, subdivision sea, or broadscale habitat type within that sea at a 0.05° × 0.05° grid, hereafter termed c-square.

Indicators	Description
Intensity (I-1)	Average number of times the area is swept per year by MBCG. Estimated as the sum of swept area for all MBCG (averaged for the six-year cycle), divided by the total area.
Proportion of grid cells fished (I-2)	The number of c-squares fished at least once in the six-year cycle (irrespective of the swept area within the cell), divided by the total number of c-squares.
Proportion of area fished (I-3)	The sum of swept area across all c-squares based on the average for the six-year cycle, where swept area in a specific grid cell cannot be greater than the area of that grid cell, divided by the summed area of all c-squares.
Aggregation of fishing pressure (I-4)	The smallest proportion of c-squares in the area where 90% of the total swept area occurs.
Persistently unfished areas (I-5)	The number of c-squares persistently unfished in the six-year cylce (irrespective of the swept area within the cell), divided by the total number of c-squares.
Impact (I-6)	Average fishing impact across c-squares (averaged for the six-year cycle).
Proportion area with impact <0.2 (I-7)	The proportion of c-squares with an average impact below 0.2 (averaged for the six-year cycle)

Data limitations in Greater North Sea sub-region

The peak in fishing intensity in 2016 and the drop in 2017 are based on erroneous data inputs. There is some information of value of landings missing in the Northern North Sea/Norwegian Trench. Impact indicators (L1 and PD) could not be calculated for c-squares > 200m depth because of data unavailability.

Temporal patterns in fishing activity are available from 2009 for vessels over 15m and from 2012 for vessels over 12m. Temporal variation in fishing activity hence represents vessels over 15m (2009-2011) and vessels over 12m (2012-2018). The assessment maps and indicator values produced are based on an average for 2013-2018.

How are changes in the fishing footprint analyzed?

To describe the fishing footprint, we expressed fishing intensity as swept-area ratios (SAR). The swept area is calculated as hours fished x average fishing speed x gear width. The gear width is estimated based on relationships between average gear widths and average vessel length or engine power (kW), as stated in Eigaard et al. (2016) and using ICES expert input. The swept-area ratio is the sum of the swept area divided by the area of each grid cell (c-square). Therefore, the C-square SAR value indicates the theoretical number of times the entire grid cell has been swept if effort was evenly distributed within the cell. For example, a SAR of 2 means that each location within the c-square is fished 2 times over the year, a SAR of 0.5 means that each location within the c-square is fished once in two years. Due to data availability, all analyses of the fishing footprint do not account for sub-grid variation of fishing events within the c-square.

In order to better understand the relationship between catch/value of landings and the levels of physical disturbance for MSFD purposes, the analysis considers ten gear groupings (hereafter termed métiers) together with the total intensity of all gears (Table 2).

Table 2 Gear groupings used in the analysis. Note that OT_CRU includes OT_MIX_CRU and OT_MIX_CRU_DMF, and, OT_MIX includes OT_MIX_DMF_BEN and OT_MIX_DMF_PEL.

Métier	Main.gear.type	Target.species.assemblage.group	Main.target.species	Depletion.rate
DRB_MOL	Dredge	Molluscs	Scallops	0.200
OT_CRU	Otter trawl	Crustaceans	Nephrops, Pandalus, mixed fish	0.100
OT_DMF	Otter trawl	Demersal fish	Cod or plaice	0.026
OT_MIX	Otter trawl	Mixed fish	Mixed fish	0.074
OT_SPF	Otter trawl	Small pelagic fish	Sprat or sandeel	0.009
SDN_DMF	Danish seine	Demersal fish	Plaice, cod	0.009
SSC_DMF	Flyshooter (seine)	Demersal fish	Cod, haddock, flatfish	0.016
TBB_CRU	Beam trawl	Crustaceans	Brown shrimp	0.060
TBB_DMF	Beam trawl	Demersal fish	Flatfish	0.140
TBB_MOL	Beam trawl	Molluscs	Whelk, snails and scallops	0.060

How is benthic impact evaluated?

Two indicators of benthic impact were used.

The first indicator of impact estimates the amount of benthic biomass, relative to carrying capacity, which will not exist in the ecosystem if the current trawling intensity continues for a long time. This indicator is estimated using a population dynamic (PD) method (Pitcher et al., 2017, ICES 2018, Hiddink et al., 2019). The PD method uses explicit estimates of the removal of benthos by a single trawl event, and explicitly relates longevity to recovery rates. These parameters were estimated from all globally available trawl impact studies for infauna and epifauna (Hiddink et al. 2017, 2019). The PD method combines information on total benthic biomass (which is linked to the overall functioning of the ecosystem, see WGFBIT report 2018 section 3.2.1 on page 57) with the relative abundance of different longevity classes that in turn relates to the structure and biodiversity. For the calculation of PD-impact, the depletion of benthos by a single trawl event will differ between the different métiers based on the penetration depth of the métiers (Table 2, see further Hiddink et al. 2017, Rijnsdorp et al. 2020).

The PD method does not account for declines of rare and vulnerable species that managers may want to protect (e.g. within Descriptor 1: diversity). Rare and sensitive species are potentially heavily affected by trawling even though the structure and function of a community is largely unaffected. To account for rare and sensitive species, we included a second benthic impact indicator which is more precautionary (L1). This indicator assumes that a population is affected by trawling if animals are disturbed by trawls during their life span. Only species in the community with a longevity less than the average interval between two successive trawling events, based on the swept area ratio, will not be affected (Rijnsdorp et al. 2020).

For both indicators, sensitivity of the benthic community is estimated from the longevity of benthic fauna in the community, i.e. the more long-living organisms the higher the vulnerability. Predictions of longevity, and hence impact, are available for the North and Baltic Sea, based on the present unfished reference condition of infauna and small epifauna, as collected by boxcore and grab samples (Rijnsdorp et al. 2018, van Denderen et al. 2020). The unfished reference condition does not take into account what could have been present in the past. It thus prioritizes areas that are at present sensitive to bottom trawl disturbance and directly benefit from protection.

References

Eigaard O.R., Bastardie F., Breen M.l., Dinesen G.E., Lafargue P., Nielsen J.R., et al. 2016. Estimating seafloor pressure from trawls and dredges based on gear design and dimensions. ICES J. Mar. Sci. 73(1): 27-43 https://doi.org/10.1093/icesjms/fsv099

ICES 2017. EU request on indicators of the pressure and impact of bottom-contacting fishing gear on the seabed, and of trade-offs in the catch and the value of landings. ICES Special Request Advice, eu.2017.13. 27 pp. https://doi.org/10.17895/ices.advice.5657.

ICES. 2018. Interim Report of the Working Group on Fisheries Benthic Impact and Trade-offs (WGFBIT), 12–16 November 2018, ICES Headquarters, Copenhagen, Denmark. ICES CM 2018/HAPISG:21. 74 pp.

Hiddink, J. G., Jennings, S., Sciberras, M., Szostek, C. L., Hughes, K. M., Ellis, N., Rijnsdorp, A. D. et al. 2017. Global analysis of depletion and recovery of seabed biota after bottom trawling disturbance. Proceedings of the National Academy of Sciences of the United States of America, 114: 8301–8306. https://doi.org/10.1073/pnas.1618858114

Hiddink, J. G., Jennings, S., Sciberras, M., Bolam, S. G., Cambiè, G., McConnaughey, R. A., Mazor, T., et al. 2019 Assessing bottom-trawling impacts based on the longevity of benthic invertebrates. Journal of Applied Ecology, 56: 1075–1083. https://doi.org/10.1111/1365-2664.13278.

Pitcher, C. R., Ellis, N., Jennings, S., Hiddink, J. G., Mazor, T., Kaiser, M. J., Kangas, M. I., et al. 2017. Estimating the sustainability of towed fishing-gear impacts on seabed habitats: a simple quantitative risk assessment method applicable to data-limited fisheries. Methods in Ecology and Evolution. 8: 472–480. https://doi.org/10.1111/2041-210X.12705.

Rijnsdorp, A. D., Bolam, S. G., Garcia, C., Hiddink, J. G., Hintzen, N. T., van Denderen, D. P., and Van Kooten, T. 2018. Estimating sensitivity of seabed habitats to disturbance by bottom trawling based on the longevity of benthic fauna. Ecological Applications, 28: 1302–1312. https://doi.org/10.1002/eap.1731

Rijnsdorp AD, Hiddink JG, van Denderen PD, Hintzen NT, Eigaard OR, Valanko S, Bastardie F, Bolam SG, Boulcott P, Egekvist J, Garcia C. 2020. Different bottom trawl fisheries have a differential impact on the status of the North Sea seafloor habitats. ICES Journal of Marine Science. 77(5): 1772-86. https://doi.org/10.1093/icesjms/fsaa050

van Denderen, P.D., Bolam, S.G., Friedland, R., Hiddink, J.G., Noren, K., Rijnsdorp, A.D., Sköld, M., Törnroos, A., Virtanen, E.A. and Valanko, S., 2020. Evaluating impacts of bottom trawling and hypoxia on benthic communities at the local, habitat, and regional scale using a modelling approach. ICES Journal of Marine Science. 77(1): 278-289 https://doi.org/10.1093/icesjms/fsz219